Chemical P H E N O M Ena in Life - Forgotten Books

HAR PER ’

S L IB RARY of LIV ING THOUGHT

CHEM ICAL

P H E N O M E NA

IN LIFE

FREDERICK CZAPEKM DJ MDN

PROFESSOR OF PLANT PHYS IOLOGY

IN THE UN IV ERSITY OF PRAGUE

HARPER BROTHERSLONDON AND NEW YORK

4 5 ALBEMARLE STRE ET, W.

19 1 1

BIOLOGYLIBRARY

G

PREFACE

T has given me great pleasure to accept thesuggestion of the Editor of Harper ’s Library

o f Living Thought , that I should treat in a volumeof this series some phases in the life processes ofplants .There is scarcely any other question in thebiology of plants of greater interest than thatof the general chemistry of the cell , viz . of theliving protoplasm , which has been so successfullyworked at by the biochemists of our time . Not

only very important results,but also most sug

gestive hypotheses , render this chapter of plantPhysiology more attractive than any other . Themolecular structure of living pro toplasm , as wellas organic synthesis in cells and the hithertoinexplicable phenomena of endosmosis in the cell ,have been rapidly placed in the foreground ofmodern scientific problems and now range amongthe great questions of biology to solve which is awell - grounded hope .So I could not resist the temptation to give ashort review of this territory of Biology which is sofull of suggestions and attractions . I was

,however

,

Vll

2285 1 5

PREFACE

not unconscious of the difficulties met with inlaying all the questions mentioned above before awider circle of readers who have not devotedthemselves especially to physiological work inbiology . A fair knowledge of physics and chemistry , both organic and physical , is requiredbesides the great number of biological facts whichmust be remembered when we try to obtain asatisfactory survey of the general physiology ofthe plant . It is therefore rather difiicult topresent the subj ect of our book in a condensedbut clear and rather popular form , and I mayexpress my doubts as to whether it can be doneat the present day as perfectly as had been mywish .

So I must beg my readers to be indulgent if myintentions have not been carried out as I wouldhave desired . At least no one will finish the bookwithout the feeling of satisfaction that ModernScience is going to touch on problems so loftythat before our days their solution could neverhave been dreamed of .

UmvaRsrrv OF PRAG UE ,

j une , 19 1 1 .

CHAPTER

I I .

I I I .

IV.

VI .

VI I .

VI I I .

IX .

CONTENTS

PREFACE

B IOLOGY AND CHEM I STRY

PROTOPLASM AND ITS CHEM ICAL PROPERTIES

PROTOPLASM AND COLLOID - CHEM I STRY

THE OUTER PROTOPLASMATIC M EMBRANEAND ITs CHEM ICAL FUNCTIONS

CHEM ICAL PHENOMENA IN CYTOPLASM ANDN UCLEU S OF L IVING CELLS

CHEM ICAL REACTIONS I N LIV ING M ATTER

VELOCITY o r REACTIONS I N L IV ING CELLS

CATALYS IS AND THE ENZYMES

CHEM ICAL ACTIONS ON PROTOPLASM ANDITS COUNTER - ACTIONS

CHEM I CAL ADAPTATION AND INHERITANCE

PAGE

62

72

Jae , J )

‘

J,

a s 9 0 9 6 0 0 d 9 0 “

CHEM ICAL PHENOM ENA

IN LIFE

CHAPTER I

B IOLOGY AND CHEM ISTRY

HE establishing of the close connection of thebiological and the chemical methods of in

vestigation ,so familiar in our days to all who are

interested in science,was by no means an easy

achievement . On the contrary , this was one ofthe most important and most difficult steps takenin the glorious era of the great French Encyclopaedists and Philosophers . Chemistry aims atshowing the diversity of matter . It tries toseparate and to select

,to outline the general laws

of proportion in quantity and weight in matter,

and it does not appeal directly to our senses .It is only experiments that step by step unveil theclouded path of the investigator and lead him upto the heights from whence he has a clear and farreaching View over the silent fields of Nature .

Chemical and physical experiments are said toShow the laws of Nature . But what do we call

B I

CHEM ICAL PHENOMENA IN L IFE

Laws in Chemistry and Physics " I f theconditions of a certain kind of experiment arekept exactly the same , the experiment must invariably le ad to the same result . Thus the sameresult is s hown , however often a physical orchemical phenomenon of a certain kind is repeatedin Nature itself or by the hand of the experimenting scientist . Single results , as they are producedby arbitrary human action , vary . In a greatnumber of them we may already distingu ish aconsiderable number Of average values . Supposethis action is repeated infinitely often , mathematicsteach us that we may consider the average resultas the true and final value , and we may believe

'

this an equivalent of a Law 0/ N ature. We see ,therefore

,that Law in Chemistry and Physics

is the expression for the probability of the resultwhen a process repeats itse lf infinitely often .

Thus a phenomenon in N ature , such as the freefalling of bodies or the chemical reaction betweensodium chloride and nitrate of Silver

,may with the

greatest certainty be expected to take in everycase the same course which we have observed evenupon only one occasion . Chance and probabilityare there excluded

,and the full certainty of a

Law ofN ature is given . Chemistry in consequencemay apply the means of mathematical calculation to the course

,and the final results of chemical

change in matter . It belongs , as we say , to theExact Sciences .

BIOLOGY AND CHEM ISTRY

Biology presents in every line a striking contrast to Chemistry. It does not need experi

ments to such an extent as ChemIstry does.Chemical obj ects lie unchanged before us , theirqualities unaltered

,unless we disturb them by

experiment . Animated N ature works upon oursenses in the most striking manner. In animalsand plants gay and bright colours delight oureyes . How much too do we not feel attractedby the different forms of movement in livingbeings " In the childhood of the civilisation ofmankind , as well as in that of the individual , Li feand Motion ,

without any Visible external agency,

are nearly identical conceptions . The variability ofphenomena in animated Nature which are accessible to mere observation without experimentsis so great , so infinitely great , that the method ofexperiment in Biology seemed to be entirelyunnecessary to all great naturalists up to theeighteenth century . Much more attention wasgiven to the comparison of the different phenomenaof life . This method is what we in our days callComparative B iology. This branch of Biology isparticularly occupied with the study of the formand the structure of organisms , that is , M or

phology and its annexes , Embryology ,Anatomy,

and H istology.

The more we feel the importance and preponderance of Morphology and of comparativeinvestigation in Biology , the more we must in

CHEM ICAL PHENOMENA IN LIFE

cline to the highest admiration for the geniuswho first applied chemical and physical methodsto Biology . Stephen Hales

’

Statical Essays

( 1 727) are the memorial of the entrance ofPhysiology into the ranks of the Exact Sciences .These Essays contain the first application ofphysical laws to biological problems . The pressureof blood in the arteries and the pressure of sapin the vessels of plants were henceforth facts expressed in exact mathematical values . In studyingHales

’

Statical Essays we may most strikingly feelthe splendid progress in Biology which lies in theapplication to the ever - changing living organismof methods hitherto only applied to inanimatematter . Experimental Biology entirely abstractsfrom the qualities which to the naive eye of theobserver are characteristics of life . I t enters theterritory of its investigation from the highes tphilosophical point of View , that of the probableconnection of living and non - living matter .Thus was built the bridge between Exact Scienceand Biology . At present we may consider Ex

perimental Biology an Exact Science as well asPhysics and Chemistry . All employ the samemethods

,and their end is the same

,viz . to lead

by means of mathematical conclusions to generalresults which enable us to explain a greater complexof facts starting from a limited number of experimental results . I would prefer to speak of Ex

perimental B iology rather than of Physiology,as is


usually done . The very experiment is what ischaracteristic of the physiologist ’s method , in thesame way as comparison is the chief characteristicof Morphology or Comparative Biology.

We Shall not be surprised to first find physicalmethods in predominance upon the field of Ex

perimental Biology . This was in the age of N ewton .

Some decades later the work of Lavoisier in France ,of Cavendish, P riestley,

and I ngenhonsz in England ,and of Scheele in Sweden brought the dawn ofscientific Chemistry . I t was not a mere chancethat the discovery of oxygen was closely connectedwith the important discovery of the fact thatliving green plants produce in bright sunlight aconsiderable amount of the newly discoveredgaseous element . We henceforth see Chemistryand Physiology growing as sister - sciences , and noera of Plant - Physiology was richer in importantdiscoveries than that of the foundation of modernchemistry inaugurated by the great Lavoisier.

At the same time that Chemistry was born ,

B iochemistry , or the knowledge of Chemical Phenomena in Life

,came into being .

Every extraordinary advance in Science wasaccompanied by a revival of materialistic philosophy . The age of N ewton,

Lavoisier, D’

Alembert,

and M anpertnis was the mother of La M ettrie’

s

work L ’

Homme M achine. A century and ‘a halfbefore our days imaginative minds even thoughtof a chemical synthesis of living cells . When


Goethe’

s poetical genius created Wagner, Faust’s

famulus , mysteriously mixing hundreds of sub

stances in his retort upon the chemical hearth ,

denn aufM i schung kommt es an,

i t was the reflection upon the great:poet of myriadsof scientific phantasms of that time , as to whetherit were not within the reach of possibility to compound Life itself from the elements which Chemistry had shown to be the pillars of the Universe ,and which were contained in every animate andinanimate part of the visible world .

Again , further , the renaissance of Materialismin the last century was the consequence of themarvellous progress of Exact Science , which evenshowed us the elementary structure of planetsand fixed stars , and taught us to construct in thelaboratory the vital compounds of animals andplants, such as sugar , fat , and protein bodies , fromtheir very elements .Here I need not give an extensive sketch of the

N atural Philosophy of our time in its relation toBiology

,and especially to Physiology . Only a

few remarks on the importance of experimentalphysical and chemical methods in Biology may beadded . The enormous advance of our chemicaland physical knowledge of the life process mayeasily lead to too far - reaching opinions on theunique significance of these methods . Can Li/e beexplained by Physics and Chemistry " Are our

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compounds in non - living matter , form a strikingcontrast . We are , then ,

not surprised to see thatat the beginning of the last century the View wasgenerally adopted that carbon compounds can onlybe formed by synthesis in the living cell . To becomplete it must be mentioned that still in theeighteenth century even the mineral salts in plantswere said to be formed in the plant cell by the LifeProcess . Saussure , in 1 804 ,

was the first biologistwho proved unquestionably that all mineral saltsare taken up into the plant from their waterysolution in the soil , and that none are formed in theplant itself .In 1 828 the question of carbon compounds in

living organisms was solved by the discovery of theGerman chemist Woehler, that urea can beartificially prepared in the laboratory fromammonium cyanate . The deep impression produced upon the scientific world by this importantsynthesis may be gathered from the opinion expressed by Dumas in 1 836 . The eminent chemiststated that no sharp line of distinction could bedrawn between Inorganic and Organic Chemistry .

In plants and animals must rather dwell a peculiarpower of synthesis which it was henceforth thetask of Organic Chemistry to imitate . Theglorious range of organic syntheses during the lastcentury is still fresh in our recollection . N earlyall the important animal and vegetable substances are at present accessible to artificial

8


synthesis fromtheir very elements . Even proteinmatter seems to have lost its mysteries since welearned from Emil Fischer ’s work that aminoacids can be combined in the same way as theyoccur in protein . Compounds of amino - acidscan be obtained which show all the main reactionsof protein substances . Emil Fischer

,of Berlin

,

was the same chemist who in 1 886 discovered howto prepare grape sugar from glycerin . A considerab le number of plant alkaloids have been alsoartificially prepared in the course of the last fivedecades . The most important colouring matters ofplants , for instance , alizarin and indigotin ,

are nolonger extracted from plants for technical purposes , but are accessible from the products of coaltar . We see , then , that animal and plant substances are by no means peculiar to the realm oforganic nature . They are compounded within theliving cell and without it by the same chemicallaws . Our task in experimental Biology can onlybe this , to explore the material in the living cellwhich carries out the chemical changes in substances , and to control the reactions which takeplace in Life .

The following chapters try to Show what successhas been attained in the endeavours of Sciencein the bordering territories of Chemistry andBiology .

CHAPTER I I

PROTOPLASM AND ITS CHEM ICALPROPERT IES

URING its life and in the course of its evolution , the form of the body and its organs

is subj ected to a continuous series of changes .But at the same pace the organism of the individual undergoes chemical changes . Its generalcomposition is changed . Chemical analysis showsnew substances formed , which at an earlier agewere not yet present , whereas some substanceshave disappeared . This is the parallelism ofmorphological and chemical change in the lifeof the individual .Chemical investigation , however , to a certain

extent teaches considerably more than Morphology does . We shall prove this in our discussion ofchemical reactions in living matter .Chemical changes in living substance con

tinne without interruption as long as activelife prevails . So the chemist has to face greatdifficulties when examining z-living matter . Fromhis occupation with inorganic matter he will beaccustomed to see that no change takes place in

10

PROTOPLASM

the matter under investigation unless an experi

ment be made .We stand before the quest ion as to what may be

made responsible for this continuous change ofform and of chemical properties .Inspection with the naked eye could not have

brought any solution of this question . Nor was

chemical analysis able to contribute facts ofimportance . Only to the microscopical investigation of the cells do we owe our knowledge of theorgans of life . And here again animal cells haveproved to be much less accessible for searchinganalysis than the cells of plants . It was in 1 840

that Hugo von Mohl , of Tiib ingen, drew attentionto the important fact that plant cells have thequalifications of life only as long as they containa slimy layer along the cell wall

,which layer was

at first called the Primordial Utricle. The thoroughexamination of anatomical facts led Mohl andSchleiden to the conviction that all the organsof the cell originate in this slimy matter . Con

sequently the mucous layer was called Protoplasm.

In the following decades it was fully establishedthat the presence of life is extremely closelyconnected with the presence of active protoplasm .

The physiologists Bruecke and Kuehne may becalled the originators of the View now universallyadopted that Protopla sm is the Living Substancein animals and plants . The general and fundamental properties of protoplasm in both are the

1 1


same . But it was the merit of the well - knownbotanist Ferdinand Colm ,

of Breslau,that he

was the first to declare,in 1 850,

the identity of theprotoplasm in plant cells and of the so - calledSarcode in animal cells .The Chemistry of Life may henceforth be called

the Chemistry of Protoplasm . This is our territorywhen we s tudy Chemical Phenomena in Life .

The first work the chemist does when beginninghis examination of a Substance , is to describe itsproperties before they have been changed by anyreaction . We have also to specify the chemicalqualities of the substratum of life before we enterupon the effects of reactions between protoplasmand other substances brought into contact with it .What is protoplasm chemically so called" I s

it to be considered as a substance peculiar toliving organisms and responsible for all the uniquephenomena by which life is characterisedOr is protoplasm a combination of differentsubstances peculiarly composed " Or, finally , isthere any unknown structure in the mucous matterwhich we call protoplasm , and should we not prefer to speak

,rather than of a substance or of a

combination of substances,of a minutely structured

organ when we deal with protoplasm "

Morphology,however

,and comparison with

other details of cell structure strongly uphold thetheory that protoplasm is an intricately constructed organ of the cell . I t does not matter

1 2

PROTOPLASM

that even the powerful microscopes which the advanced technical perfection of our time has produced,

cannot show any more minute morphologicaldetails in protoplasm than some very small darkgranules or scarcely Visible drops of liquid

,spoken

of as M icrosomes . But the exact and extremelyregular development in the evolution of the cellorgans

,as well as the undoubted co - operation of

protoplasm and the nucleus in cell cleavage andin fecundation

,is the strongest affi rmation of the

organ - theory of protoplasm . In consequence ofthese facts

,we prefer to speak of Cytoplasm in

stead o i protoplasm , when we characterise theliving substance of the cell , surrounding thenucleus .Experiment

,too , seems to establish such a theory

very readily . When animal or plant tissue isminutely pounded in a mortar

,the pulpy mass

which we finally obtain is far from being anorgan

,or from containing living cells . It is as

little a living thing as a watch remainsa watch after having been ground down topowder . N otwithstanding this , the componentsubstances must have remained in either case .

I t is clear that protoplasm is as little identicalwith its component substances , for instance ,protein bodies

,carbohydrates , etc as pulverised

gold,steel

,and rubies are identical with the

mechanism of a watch . This consideration mustlead us to the conclusion that protoplasm is not a

I 3


mere orderless homogeneous combination of different substances or a peculiar substance initself. On the contrary , it renders it very probablethat structural characteristics play a most important part in living protoplasm , perhaps formthe essential trait in the organ of cell - life . Ex

perimental Biochemistry of our days , however , hasbeen able to show that the characteristics of livingprotoplasm are not all destroyed at once , when aliving organ is ground to a pulp . I f care is takento ward off the effects of microb es which rapidlydevelop in the remains of the tissues , by addingsome toluol or chloroform , a series of reactionswhich are quite peculiar to life can be still observedin the disorganised pulpy masses . This method ofpreserving organs which have been minutelyground down is much employed in modernphysiology . We call it Autolysis . It is possibleto prove that autolytic mixtures show the samechemical processes as we find in the digestion offood

,in respiration and even in excretion . There

fore we cannot concede that protoplasm is atonce destroyed when it is ground down as minutelyas possible . The death of protoplasm is no suddenprocess . The reactions of life cease Slowly andsuccessively one after the other .Theories which maintain that protoplasm is

merely effective in life through its structure aregenerally classified as the Engine- Theories ofLife.

We see that such theories are right essentially ,

14



different organic bases,

finally mineral salts ofpotassium

,magnesium , and calcium .

Reinke and Rodewald drew from their differentexperimental work the conclusion that protoplasmcould not be considered to be a specific organicsubstance . It was rather a complex of variousorganic and inorganic substances , none of whichwas new to chemistry . In consequence of theseexperiments the two German biologists inclinedto the opinion that it was not chemical and sub

stantial properties which essentially characterisedprotoplasm

,but mainly the structure of the

protoplasmatic masses in living cells .The impression made by this experimental workupon biologists

,both botanists and zoo logists

,

was so great that for a long series of years theEngine or Structure- Theory of protoplasm wasexclusively the prevailing one . The opinion ofOscar Loew and some other eminent physiologiststhat protoplasm must nevertheless contain somepeculiar matter which is characteristic of life wasscarcely taken up by any textbook authors orUniversity teachers .The last decade

,however , seems to have pre

pared an alteration in the course of the biologyof protoplasm . As I have already mentioned ,

chemical methods clearly show that in the pulpprepared by gri nding down living organs in amortar some vital phenomena continue for alonger time . Therefore not all the Chemical

16

PROTOPLASM

Life is destroyed , even if cell - structure is as completely as possible annihilated . Consequently somesubstances must exist in protoplasm which aredirectly responsible for the life - processes , whichdo not cease with the destruction of the cel l .And these substances are characteristic of livingprotoplasm . For when the cell - pulp is heated tothe temperature of boiling water these chemicalprocesses cannot be any longer observed . Theremainder of the cells may then be considered as

definitely dead .

So we must come to the conclusion that , inspite of the ingenious experiments and argumentso f Reinke and Rodewald , the comparison betweenprotoplasm and mechanical structure is not quitean exact one . No mechanism is known whichwould not be destroyed by minutely pounding it

,

but which is destroyed by boiling water . And,

on the other hand , chemical alterations are quiteusually caused by a raised temperature , butscarcely in any case by simply grinding downthe material . When we see that the substancesin living protoplasm are so easily destroyed byheat , we are not surprised that the analysis ofprotoplasm by Reinke and Rodewald could notdetect such constituent parts of living matter . Atpresent , however , it would be possible to carryout exact analytical studies on protoplasm withhighly developed methods and with much moresuccess . N evertheless , the literature of the last

0 I 7


years does not contain more than a few reportsabout analytical work on protoplasm . The greatdifficulty in such investigations is to procure asufficient quantity of suitable material .N evertheless

,we possess valuable papers on

the chemistry of protoplasm from special researchwork done on animal and plant material . Thereare results which clearly Show the difficult iesmet with in preparing the protoplasm - proteinswithout any chemical change during the process ofseparating them . There is no doubt that protoplasm contains highly complex proteins whichare very easily split up into more primitive proteinsubstances

,even by treating them with very

dilute alkaline or acid solution,or even by keeping

them in a watery solution for a couple of hoursat ordinary laboratory temperature . Reinke ’sopinion was that one of the protein b odies of hispreparation

,the so - called Plast ine , was the chief

constituent of protoplasm . Later , Etard wasfortunate enough to isolate complex protoplasmproteids of highly variable character . TheFrench chemist proposed to name these compounds Protoplasmids . By more advanced methodsof quickly drying the cell protoplasm withoutapplying too high a temperature , zoochemists

succeeded in preparing a series of such OrganP roteids . We cannot but hope that the biochemistry of protoplasm will in this way make considerab le progress . The successful investigations

18

PROTOPLASM

on the Enzymes marked a very important steptowards the discovery of the true chemical natureof protoplasm . A special chapter has to bededicated to these remarkable substances

,the

properties of which are eminently characteristicof living matter .The final result of our discussion is that thereare many reasons for maintaining that protoplasmreally is of a peculiar chemical constitution

,and

that it does not merely represent a mechanicalstructure . But we have to concede that thechemical nature of protoplasm is not foundedupon the peculiarities of one particular substancewhich is characteristic of living protoplasm . Thereare

,we are certain of it , a great number of con

stituents of protoplasm which form the substratumof cell~life .

CHAPTER I I I

PROTOPLASM AND COLLO ID- CHEM ISTRY

E have been told in the foregoing chapterthat protoplasm is a slimy mass contain

ing numerous organic compounds which chieflybelong to the groups of proteins

,carbohydrates

,

and fatty bodies . The substances named hererepresent for the chemist chemical bodies ofcertain physical properties which

,since the

famous investigations of Thomas Graham onLiquid Difiusion applied to Analysis , in 1 861

,are

well known as colloidal properties . Colloids , theprototype of which is glue , H il da

, were characterised by Graham as substances which scarcelyor not at all Show diffusion through animal membranes , and which cannot possibly be brought intothe shape of crystals . Colloids , therefore , form astriking contrast to the common mineral saltswhich readily show diffusion or Osmosis throughmembranes , and which regularly appear as crystalswhen the solution is concentrated and evaporated .

G raham spoke of this stage as the CrystalloidStage. For him

,to use his own words

, Colloidsand Crystalloids were two worlds of matter ,quite distinct and without any transition from oneto the other .

COLLO IDS I N PROTOPLASM

It marked an important progress in Biologywhen the Views of Thomas Graham were applied toprotoplasm . The manifestly colloidal nature ofliving protoplasm demonstrated ad oculos theSignificance of studies on colloids for Biology.

Protoplasm shows itself as an almost liquid slimeof the consistence of a liquid starch - paste or of astrong solution of albumin

,and neverbecomes solid .

Graham divided colloids , according to their moreliquid or more j elly- like consistence , into Sols andGels . There is no doubt that protoplasmhas thenature of a sol. While the knowledge of saltsolutions was being perfected in the ’seventies and’eighties of the last century , colloidal solutions orsols were also extensively studied . So it waslearned that colloidal sols differ from salt or truesolutions in a number of important points . Saltsolutions are always electrolytes , colloidal solutionsnever are . Salt solutions have a lower freezingpoint and a higher boiling - point compared with themedium of solution (water) . Colloidal solutionsdo not Show any divergence from the two principalpoints of temperature of the medium of solution .

Modern physical chemistry explains the properties o i true solutions by the hypothesis that

,

depending upon dilution and temperature , a largeror smaller number of the dissolved molecules aresplit up into smaller particles which are identical with Faraday ’s I ons. Colloidal solutionsdo not conduct electric currents and do not Show

2 1


any difference in the osmotic pressure theoreticallycalculated from the number of molecules . So wemust believe that colloidal solutions are neverelectrolytes , but are always molecular solutions .The depression of the freezingpoint in solutionsis less in proportion as the molecular weight ofthe substance dissolved is greater . I f colloidalsolutions only Show a very slight depression , or onewhich lies beyond the limits of exact observation ,

the conclusion is evident that colloidal substanceshave a very considerable molecular weight . I twas extremely interesting for physiology to learnthat exactly those substances which are most important for life possess a very high molecular weightand consequently very large molecules in comparison with inorganic matter . For example ,egg - albumin is said to have the molecular weightof at least starch more than whilstthe molecular weight of hydrogen is 2 ,

of sulphuricacid and of potassium nitrate about 100,

and themolecular weight of the heaviest metal salts doesnot exceed about 300.

Thus we come to the hypothesis that the sizeof the molecules of dissolved colloids is considerablylarger than the Size of those of crystalloids . It is ofgreat interest that in living protoplasm such largemolecules are characteristic of its chemical structure .Graham believed that colloids and crystalloids

are not connected with each other by substancesof intermediate character. They were rather said



From particles which were too heavy to remainsuspended and which sank quickly to the bottom ,

a continual graduation was observed down“ to

particles which were so small that they passedthrough paper filters and were not even microscopically visible . Bredig

’

s experiments on platinum dispersed by the electric are in water clearlydemonstrated that metallic platinum may beobtained there in every imaginable size of particles .The coarsest part icles form a brown precipitate.The finest of them stain the water dark brownwithout any trace of turbidity ,

are not retainedby any filter , and no particle is microscopicallyvisible . The liquid has all the properties of acolloidal solution of platinum .

The metal - sols , of which a large number havealready been obtained , are of great interest , sincewe possess a new experimental help for s tudies ofcolloids in the so - called Ultramicroscope. Tyndalldrew attention to the remarkable phenomenon thatrays of light remain visible in a liquid only whenparticles suspended therein reflect the light . Whenwater is carefully freed from any trace of particlesof dust , we cannot follow the course of rays of lightthrough the liquid . The water rather appears to usas itself diffusely lighted without showing thestripes of light which are produced by a ray ofsunlight or electric light thrown upon a vesselcontaining water . Colloidal solutions alwaysshow Tyndall ’ s Phenomenon . This experiment ,

COLLO IDS IN PROTOPLASM

therefore , is very suitable to demonstrate theexistence of solid particles in colloidal solutions .About ten years ago Zsigmondy , in Jena , very

ingeniously used the principle of Tyndall ’s phenomenon to show the single particles themselvesin colloid solutions by means of the microscope .

Whilst microscopical obj ects are usually illumimated by rays of light so directed that they areparallel to the axis of the microscope , Zsigmondy

’smicroscope was arranged in such a manner that avery thin and strong ray of electric light wasthrown through the microscopical preparationfrom the side , vertical to the axis of the microscope . Consequently the microscopical field ofVision remained dark . The suspended particles ,when illuminated from the side , reflect the lightand become Visible , appearing like small starson the dark sky . The strong dispersion of lightdoes not permit us to recognise the size and shapeof the single particles . But they can be countedexactly . In this way the particles of platinum orof gold - sols were made visible

,and even their size

could be indirectly determined . An arrangementwas even made for studying living cells andprotoplasm by means of the ultramicroscope .

It was clearly shown that numerous particles inprotoplasm are made Visible by this method whichcould not be seen by the ordinary microscope .Ordinary microscopical observation with thestrongest lenses can Show particles of about 250mi

2 5

CHEM ICAL PHENOMENA I N LIFE

in diameter . We call particles of and above thissize M icrons . The ultramicroscope makes particles visible even down to the size of 6 pp , providedthat the power of light applied is strong enough .

Such particles are called Submicrons . But insolutions of albumin or of starch - paste even theultramicroscope does not dissolve the cone oflight into single particles . N evertheless , it ishighly probable that even in such solutionsseparate particles exist which are smaller than6 up . Such are called Amicrons . The presence ofamicrons can be shown indirectly , for suchcorpuscules readily become the nuclei of precipitates . When amicrons are present , precipitation is more easily effected than without them .

The size of 6 pp. in diameter is probably the Sizeof the albumin molecules themselves . Thus bymeans of the ultramicroscope it has been madepossible to distingu ish the largest molecules ofcolloidal substances and to demonstrate thereality of existence for the molecules . Submicrons ,however

,are generally already aggregations of

molecules . In such a way we can get at least aglimpse of the molecular structure of colloids ,and of protoplasm in particular . Protoplasm ,

in the same way as colloidal solutions , mustgenerally be considered as a heterogeneous system.

Solid particles of different colloidal substances aresuspended in a liquid . The particles are ofdifferent sizes . Some do not differ in size from


large molecules , some form aggregations of molecules

,others consist o f small masses of the sus

pended substance,others finally are but coarse

particles , already subj ected to the force of gravitation , and , if allowed ,

quietly deposit . Theparticles , besides , may be of different physicalconditions

,either liquid drops or solid bodies .

Colloidal solutions,indeed

,Show quite a different

physical behaviour if the suspended particlesvary in size and in physical condition . In thefirst case it is advisable to divide the colloidalsolutions into several groups according to thesolid or liquid state of the suspended particles .Colloidal solutions which contain solid particlesmay be called Suspensions , such as contain smallsuspended drops of liquids may be named Emulsions . Instead of drops there may even occur incolloids small bubbles of gas . Then the colloidsystem more or less resembles froth . It is possiblethat even in protoplasm small bubbles of gas areincluded , forming a very fine foam .

According to the Size of the suspended particles ,all these colloids Show well—marked physicaldifferences . When the particles are comparativelylarge the constitution of the system is as a rulevery unstable

,and the particles are inclined to

deposit . Such suspensions are scarcely to be considered as colloidal systems , but rather as a transition stage to colloids . Protoplasm must to acertain extent have the properties o f such a sus

2 7


pension . We must therefore ask what characteristics are found in these suspensions . Suchsystems have in general the properties of theliquid medium . The specific weight

,viscosity ,

and surface tension do not differ from the valuefound for the medium

,and so it is with regard

to the freezing - point,the boiling - point

,and the

power of conducting electric currents . We mayunderstand this to be due to the comparativelysmall quantity of the suspended substance inproportion to the quantity of the liquid medium .

Such suspension systems do not in any way re

semble solutions . Here we may mention the socalled phenomenon of Cataphoresis in thesesuspensions . When an electric current passesthrough the suspension , the particles migrate tothe anode or to the cathode , corresponding to thespecific character of the suspension . This phenomenon , which has been thoroughly discussed byphysical chemists , has not yet shown itself to beof any great importance for the chemistry ofprotoplasm .

Whilst suspensions with comparatively largeparticles can be recognised as suspensions byordinary microscopical observation , the particlesin other colloidal solutions can be discovered onlyby means of the ultramicroscope . We havementioned that protoplasm contains ultramicroscopic particles or submicrons , which are not seenbut by ultramicroscopic investigation . All these

38


colloids may be called Suspension Colloids . Fromcoarse suspensions to suspension colloids thereexist all kinds of intermediate suspensions . Theplatinum sol and the other metal sols mentionedabove belong , according to their action and to theirphysical properties , to the suspension colloids .They have been of great use in studies on suspension colloids . Quantitative analysis showed thateven in suspension colloids the amount of thesolid phase is very small in comparison with thequantity of the liquid medium Suspension colloidshave very few points of resemblance with solutions .They do not conduct electric currents but to aslight extent

,and they do not Show alteration

from the freezing - point of their liquid medium .

Cataphoresis has been quite generally noticedeven in suspension colloids . In fact , suspensioncolloids are nothing else but cases of ultramicroscopic suspension . The only one important difference from coarse suspensions is the great stabilityof suspension colloids . Platinum sol or the colloidsolution of hydroxide of iron or any other suspension colloid may be kept for years without showingany alteration . Since the suspended particles areconsiderably smaller , we must believe that thesurface of contact between the suspended substanceand the medium (we speak nowadays of theM edium ofDispersion) is much larger in suspensioncolloids than in coarse suspensions . We may consider this to be the reason for the greater stability

29


of the former. Of great chemical and biologicalinterest is the effect of small amounts of salts

,i .e .

electrolytes , on suspension colloids . I f we preparea colloidal suspension of mastic resin in water bymixing one drop of alcoholic mastic solutionwith a large quantity of water , and add to themilky liquid a trace of mineral salt solution

,after

a couple of seconds white flakes of deposit appearin the colourless liquid , and the whole resincolloid is precipitated in flakes . We do not doubt ,and our opinion is confirmed by the noteworthyexperimental work of Hardy , Bredig , and others ,that the electric properties of the colloid play thechief part in this flaking - phenomenon . We have tothink that the colloid particles are aggregated oragglutinised by electric influence , and form adeposit when they have reached a certain stage ofaggregation . Probably the particles charged withpositive or negative electricity attract ions of thecontrary charge . Since ions have a much strongerelectric charge than colloid particles

,one ion may

attract a number of colloid particles . By this processthere must be formed large masses of the colloid ,

which are no longer able to remain suspended inthe liquid

,and form flakes which slowly deposit .

All colloid solutions or sols which do not Showany separate particles either by means of theordinary microscope or by the ultramicroscope ,are at present united under the name of Emulsion

Colloids . There is no doubt that j ust such colloids

30



negatively electric , but in acid medium they arecharged with positive electricity . Emulsioncolloids also show quite a different reaction tosmall quantities of electrolytes . Emulsion colloidsare never precipitated by a small amount ofmineral salts . The electric properties of the ionscannot alter the colloid state .Otherwise emulsion colloids in many respectsresemble real solutions . In the first place , thediffusion of emulsion colloids is considerableenough to be measured by means of the usual contrivances for studying diffusion phenomena . Suchexperiments had already been made by Graham .

Later on , Pfeffer carried out experiments onsolutions of gum - arabic and glue

,to Show that

distinct osmotic pressure can be observed to beexercised by such colloids . The osmotic pressure ,however

,is very small as comparedwith the osmotic

effects of sugar solution or of inorganic salts .Even the freezingpoint of emulsion colloids is distinctly lower than the freezingpoint of the puremedium . Such sols show many transition characteristics to true solutions . The density of sols isdistinctly different from the specific gravity of thepure medium . The surface tension of sols alsodiffers regularly from the surface tension of thepure medium . In many cases the surface tensionof water is lowered by dissolving colloids in it .Such characteristics are to be expected in the

emulsion colloids of protoplasm . Protoplasm ,

32


therefore , has many of the physical and chemicalcharacteristics of true solutions . On the otherhand , properties must be present in protoplasmwhich are only found in suspensions . We see

that such a state of things is very favourablefor the action and counteraction of many sub

stances in the narrow territory of the protoplasmof one cell . Water is without doubt the medium ofsolution in protoplasm . Many substances

,chiefly

of the groups of protein bodies and carbohydrates,

form the mucous emulsion colloid which is thefundamental mass of protoplasm . Protoplasm ispractically an albumin sol. We remember thatfatty substances are regu lar constituents of protoplasm . They are not soluble in watery mediums

,

but they may be brought into the form of colloidsolution in water , either only into the stage ofsuspension colloids

,as we can see on shaking oil

and water together , or even into the stage ofemulsion colloids . The latter can be reached byadding a trace of po tassium carbonate to themixture of oil and water . It is sufficient to Shakethe mixture for a very short time to form a milkyliquid of great stability , which can be filteredwithout change . The physical properties of suchoil emulsions are . the properties of emulsion colloids .In protoplasm fats must be present in the form ofsuspension colloids and of emulsion colloids . Othersubstances insoluble in water must be present inSimilar

v

forms .

D 33


It may be that the whole mass of protoplasmis not equally rich in these suspensions . As a rulewe perceive along the cell wall on the outmostlayer of protoplasm a thin protoplasmatic partwhich does not Show any visible particles

,and

only very few under the ultramicroscope . Thislayer was named by Pfeffer Hyaloplasma . Theother parts of protoplasm usually contain greatquantities of coarser particles which give a greyishcolour to the whole protoplasmatic mass . Pfefferintroduced the name of Polioplasma for this partof the cytoplasma .

It is manifest that Hyaloplasm is an importantmedium to admit substances from outside intothe cell as well as to permit the passing out ofproducts of the cell . Hyaloplasm can therefore beconsidered to be the cell organ for the Endosmosisand Exosmosis of substances , i .e . the osmoticorgan of cell protoplasm . Polioplasm , on theother hand , must be the organ to assimilate thesubstances which enter the cell , to form newconstituents of protoplasm , to furnish differentforms of physical energy , to continue the processof life and to form the substances which aresuperfluous for cellplasm and are excretions .Polioplasm is thus the seat of the metabolismof the cell itself . We shall try to Show how far ourpresent chemical knowledge may explain theconnection of all these functions of living cellprotoplasm .

34

CHAPTER IV

THE OUTER PROTOPLASMAT IC MEMBRANEAND ITS CHEM ICAL FUNCT IONS

ESIDES the transparent condition and theabsence of coarser granules or microsomes

hyaloplasm exhibits a series of microscopicalpeculiarities . It is well known that protoplasmin living plant cells generally shows a streamingmovement which is easily recognised either by themovement of the chlorophyll bodies themselvesor by that of the microsomes . These bodies arecarried along by the streaming protoplasm withconsiderable velocity . Even the cell nucleus is insome cases carried along by the current of streaming protoplasm . This outer transparent layer iscontinually at rest , is never made turbid byparticles , and never includes drops o f liquid , cellsap , which is quite commonly found in the polioplasm of older cells . Perhaps the viscosity ofhyaloplasm is greater than that Of polioplasm. In ;any case the boundary lamella of the hyaloplasm “

must be of tougher consistence , and may be wellconsidered to be a plasmaticmembrane or boundarymembrane of the living parts of the cell . Thisplasmatic membrane is the proper organ for

35


regulating the osmotic change of substanceswith the outer world . Wh ile the cellulose membrane of the cell is only a dead cover of the livingcontents , the living plasmatic membrane isvariable in its condition and is quite differentwhen in its normal living state and when dead .

I f Slices of beet - root are dipped in water,after

having the remainder of the cells which were cutthrough properly washed off , one may keep themin water for any length of time wi thout losingeven a trace of the red colouri ng matter in theliving cells . But if chloroform is added to thewater and the cells are killed by the narcoticagent , streams of red colour go out from thetissue . The dead protoplasmatic membrane is no

"longer able to retain the contents of the cell .In the living cell the decision to take up dis

solved substances from the liquid outside the celllies with the protoplasmatic membrane . Eventhe well - known fact that the chemical constitutionof plants is quite different from that of the soil inwhich they are growing, proves the elective influence of the protoplasmatic membrane inendosmosis . This elective influence is muchbetter shown by the phenomenoh of P lasmolysis.

We owe to Hugo de Vries , of Amsterdam , theexcellent method here described . It is best tochoose cells with red - coloured cell sap for theexperiments . Such cells are found on the undersurface of many leaves . Corollary petals may also

36

THE PROTOPLASMATIC MEMBRANE

well serve the purpose , but they are not so easilycut with the razor . When such sections are putinto salt solution of sufficient concentration , e .g .

potassium nitrate 2 per cent , after some minutesall cells show their protoplasm shrunk awayfrom the cell wall . The cell protoplasm forms ared ball lying free in the cell . When the sectionsare put back into water , the plasmolysis disappearsand the cells regain their normal condi tion .

Plasmolysis is therefore a normal , merely physicalphenomenon

,not at all a pathological one .

How can plasmolysis be explained Microscopical inspection immediately convinces us ofthe fact that the volume of protoplasm is reducedin plasmolysis . I t was only po ssible for this to bebrought about by the expulsion of water from’ thesap vacuole of the protoplast . By loss of water theconcentration of the sap is increased , until theosmotic value of the outer solution is greater thanthe osmotic value of the cell sap . This state beingarrived at , equilibrium is regained . We learnfrom this process that the protoplasmatic membrane cannot be permeable for the salt in solution .

I f it had been permeable , the equilibrium wouldhave been reached simply by endosmosis into thecell

,as long as the concentration inside and outside

had not become equivalent . Or osmotic substanc’eswould have penetrated the protoplasmatic membrane from the inside of the cell when plasmolysisdisappeared in water . Consequently , we may say

37


that the plasmolytic power of a certain solutionproves distinctly that the substance cannot passthrough the living protoplasmatic membrane .I f the solution does not effect any plasmolysis ,we may be sure that the substance enters the cellmore or less considerably .

Ernest Overton was the first who thoroughlyinvestigated these interesting problems in 1895 .

He found that mon - acid al cohols, aldehydes ,

and ketones,also es ters of fatty acids and

alkaloids , produce least plasmolysis . As a ruleit is impossible to bring about plasmolysis bymeans of these substances . They enter the cellvery easily and pass through the plasmaticmembrane without any difficulty . G lycols andamino - compounds cause plasmolysis a little morereadily . With glycerin or erythrite it is stilleas ier to bring about plasmolysis . But the sugarsand the substances most closely related (forinstance

,mannite) , the amino - acids and the salts

of organic acids very readily produce plasmolysis .They cannot pass through the protoplasmaticmembrane but with great difficulty . Finally , thesalts of inorganic substances very quickly causeplasmolysis

,since they very slowly pass the

plasmatic membrane , or practically do not passthe boundary of protoplasm . Overton added to hisvaluable experiments a most ingenious conclusion .

He drew attention to the fact that just suchsubstances easily pass through the protoplasmatic

38



preparing for the resting state . Plasmolysedprotoplasm has the same inclination . We see

that protoplasm in rest has the tendency todiminish its surface as far as possible inproportion to its mass or its volume . Thespherical surface is the geometrical minimum ofsurface for a certain volume . From this phenomenon we learn that the force of surface tensionmust in some way regulate the outlines of livingprotoplasm . When the living protoplasm of anamoeba stretches out its so - called Pseudopodiaon one side

,and draws in the proj ecting parts on

the other , thus creeping slowly over the moistground , variations in the surface tension ondifferent parts of the circumference of the cellmust take place . The surface tension must increasewhen new prominences are formed , and surfacetension must diminish whenever Pseudopodiaare drawn in . But such alterations in surfacetension presume certain chemical changes in theboundary layer of the cell

,and formation of

substances which Show different surface tension incomparison with the foregoing state . We learn ,

further , that such chemical processes must bereversible

,to be repeated whenever needed in cell

life . In water protoplasm always Shows a d istinctly lower surface tension to the watery mediumthan mucous protein substances or carbohydrates .It always rounds to spherical shape when inrest .


We owe to the famous thermodynamic studiesby Willard G ibbs , the eminent American scientist ,the theoretical basis for the knowledge of thebehaviour of different substances in compoundsystems which possess different surface activity.

I f these substances have the power of diminishingthe surface tension of the medium

,they always

Show the tendency to accumulate on the surface .

I f there are several such substances , then thatSubstance which most depresses the surfacetension , or is most surface - active , is generallyaccumulated in the surface layer . Upon thebasis of Willard G ibbs ’ theory we may expect inadvance that all the protoplasmat ic substanceswhich have the strongest power of depressingsurface tension , such as fats , must necessarily becollected upon the surface of protoplasm . So

Overton ’s hypothesis is confirmed by severalarguments , and we may consider it to mark animportant progress in the chemistry of protoplasm .

In the course of these investigations it was highlydesirable that we should be enabled to measurethe surface tension of living protoplasm

,and to

compare the surface tension of protoplasm withthe figures obtained for the surface tension ofdifferent substances . The difficulties

,however

,

were great and could not be overcome till lately .

The advance sought for came from studies on thetoxic effects of alcohols on living cells . Traube , inBerlin , showed that the well - known law of the

4 1


poisonous effects o f alcohols , generally calledRichardson

’

s Law, that the higher members of theseries of alcohols are more poisonous than the lowerones , was connected with the capillary propertiesor the surface tension of the alcohols . The Germanchemist proved that the surface activi ty of thealcohols increases from one member to the followingone in the same series in the ratio 1 3 . A glanceat the results obtained by Overton and others onthe poisonous effects of alcohols immediatelyshowed Traube that the toxic effect increases in thesame proportion . The law of surface activityand Richardson ’s Law must therefore be the same .Later on

,corresponding facts were found in the

class of esters,but exclusively in the members

of an homologous series of organic compounds .When I studied the toxic effects of organicso lutions on plant cells I noticed that the exosmosis of substances from the cell vacuole , consequently the death of cells , regularly took placewhen the surface tension of the solution had reachedthe same degree . Most plant cells are inj ured anddie when a solution is applied which has thesurface tension of about two - thirds relatively tothat of water . N o alcohol , no ether nor narcotichas been found which did not affect the cell in asolution of such a surface activi ty . But all substances o i the most different chemical characterbegan to injure the cell j ust when the surfacetension had reached the critical point . Since all


alcohols,ethers

,ketones

,and many other sub

stances Obey the same physiological law , we mustconclude that all these substances have the samephysiological effect upon living protoplasm . I fwe consider that according to Willard G ibbs ’

theory a substance of higher surface activity ,when brought into contact with protoplasm , mustnecessarily displace the active substances of thesuperficial layer , we see that di sorganisation ofthe structure of this layer must be the conse

quence . We understand that exosmosis musttake place . This effect is always exercised whenever the concentration of the substance exceedsthe critical degree of surface tension . This degreetherefore must be slightly below the real value o fprotoplasmatic surface tension . Consequently wemeasure also the surface tension of protoplasm ,

when we apply alcohol or any other solution o fthe critical capillarity . Practically we may takethe surface tension of common plant cells asequivalent to the surface tension of 1 1 ethylalcohol .This result forces us to raise the question whythe surface tension of protoplasm has j ust thisvalue and no other . Further experiments on theworking of fatty emulsions on living cells showedme that poisonous effects such as are produced byalcohols can be caus ed even by emulsions of fattybodies , that is , by colloid solutions . The Onlycondition is that the surface tension should be low

43


enough to affect the superficial layer of protoplasm . So lecithin or cholesterin emulsionsare quite as effective as true surface - active solutions . But emulsions of neutral fats never producetoxic effects . The determination of the amount ofsurface tension in emulsions of neutral fats ashighly concentrated as possible , gave the resultthat such emulsions regularly depress the surfacetension to two - thirds of the value of that of purewater . Since fatty compounds are always presentin protoplasm , it does not seem to be by chancethat the surface tension of living protoplasmand the surface tension of fat emulsions arepractically the same . The conclusion mayperhaps therefore b e drawn that the superficiallayer of protoplasm contains an emulsion of neutral

glycerids , such as triolein ,linolein , ricinolein , and

others .Overton ’s and Quincke ’s theory that the peri

pheral layer of protoplasm can be compared to anoily film or a very thin layer of fat (Overtonthought of lecithin or cholesterin) does not seemto be quite a correct one . The ordinary food ofplants consists of watery solutions of substanceswhich are usually not soluble in fat . It is , as Ithink , more probable that the fat in the plasmaticmembrane is present in the form of an emulsionof extreme fineness . The interstitial spacebetween the fat - globules must be filled up with awatery colloid so lution , most probably a protein

44


sol. So the plasmatic membrane would in myopinion consist of two phases . One , the lipoidphase

,is given by a fat emulsion , the other , the

hydroid phase,by the protein solution which forms

the greater part of hyaloplasm .

The Theory of Osmosis , or the diffusion of dissolved substances through membranes

,has under

gone many changes . There was a time when itwas generally believed that the diosmosis of asubstance depended upon the size of the pores of themembrane and the size of the molecules of thedissolved substance . Diosmosis cannot take placewhen the pores are too small to let the moleculespass . The membrane was considered to act like asieve for the molecules . This hypothesis does notexplain why fatty substances cannot pass membranes which have taken up water . All signs showrather that solution aflinities play the mostimportant part in diosmosis . The membrane isalways permeable for a certain substance , whenthis substance is soluble in the material of themembrane . N ernst demonstrated this View by aclear experiment . Ether is soluble in water aswell as in benzene . Benzene is soluble in ether only ,and inso luble in water . When a quantity of benzene and a quantity of ether are separated fromeach other by a layer of water , it is to be expectedthat the ether will go through the layer of water ,but not the benzene . A continuous stream ofether will pass through the water , but no stream

45


of benzene in the contrary direction . An osmoticpressure must be produced , therefore , in thesystem on the Side of the benzene . When the experiment is carried out animal membrane saturatedwith water is placed , instead of a layer of liquidwater

,between the ether and the benzene . The

benzene is poured into a glass funnel connectedwith a glass tube

,and the funnel is closed with the

saturated membrane . Then the funnel is dippedinto a vessel containing ether . After a certaintime the liquid rising in the glass tube shows theendosmotic streaming in of ether , subsequently theosmotic pressure .

In the foregoing description the term PlasmaticM embrane has often been employed for the superficial layer of hyaloplasm . We have to j ustify thechoice of this expression . Membranes are films offirmer consistence than the material , viz . theliquid upon the surface of which they are formed .

80 the expression plasmatic membrane implies afirmer consistence for this layer than for thehyaloplasm itself . We know from daily experiencethat a colloidaliso lution such as a solution of albumin or starch paste

,is inclined to form a thin film

on the surface,which has almost the physical con

dition of a solid substance . Pro toplasm , being acolloidal system

,will most probably not differ from

other colloids in this respect . We notice , indeed ,

after a lesionjof a'

cell when the cell and its protoplasm have been cut through , that the surface of the

46



suspension colloids . Such precipitations are notreversible . When , on the other hand , albumin isprecipitated by sodium chloride , it is possible toagain dissolve the precipitation by diluting itwith water . This process is reversible . Generallyin album in all precipitations with the salts of thelight alkaline metals and of magnesium arereversible . But they are not reversible whenprecipitated by copper salts , iron salts , or any othersalt of heavy metals . Precipitations with calciumor strontium salts are inclined to be quite insolublein water . It is noteworthy that the working of thesalt depends upon the acid contained in it . FrancisHofmeister , of Strassburg ,

was the first to Showthat alkaline metal salts of different acids have acertain graduated effect on colloid solutions .They may be arranged in the following way ,

beginning with the acid which precipitates mostquickly “

Citrate , Tartrate , Sulphate , Acetate , Chloride ,N itrate , Chlorate .

This law became of the greatest importance inthe chemistry of colloids . It is not only applicable to the transition of colloid solutions into solidcolloids

,but even to the chemical and physical

states of solid colloids themselves .Graham named solid colloids Gels , the name

corresponding to that of Sols or liquid colloids .

The physical condition of certain gels is verydifferent . G lue itself, when quite dry , forms a

48


horny mass,hard , inflexible , and brittle . When it

is more or less saturated with water , it becomesflexible

,viscous

,then gelatinous , and in the

course of imbibition with water it approaches theliquid state . Many gels have the character of agelatinous mass . Some , as gum - arabic , finallydissolve entirely . Others , as cherry gum , swell inwater to a j elly and never dissolve . Doubtlessgels are of great importance in plasmatic structure .They are formed in plasmatic colloids by manyinfluences , such as surface tension , electrolytes ,and the mutual precipitating effects of colloids .Wherever protoplasm sols meet precipitating influences , films must be formed , wh ich separate thedifferent parts from each other . Such gel - membranes , on the other hand , play the part of semipermeable filters . Some substances are soluble inthem , and consequently pass through ,

but othersubstances being insoluble in the gel substance areretained . There is still another retention ofsubstances in gels which is not a consequence oftheir insolubility , but , on the contrary ,

must betraced back to some affinity of the substanceretained with the gel colloid . We call this processof retention Adsorption of Substances . There isno doubt that adsorption is of the greatest importance for chemical processes in life . We haveespecially to consider that the reso rption of dissolved substances by cell protoplasm from thesurrounding liquids must be connected with ad

49.


sorption in protoplasm colloids . Taking up foodby hyaloplasm is consequently as inseparablefrom adsorption in the colloidal matter of theplasmatic membrane , as from solution in the fattysubstances of the superficial layer of protoplasm .

Essentially adsorption cannot be separatedfrom the swelling of gels in water . Many experiments have shown that all influences which furtherthe swelling of gels hinder adsorption and viceversa . Hofmeister ’s Law was found to be in forceeven in this group of phenomena . The anions ofacids which are most effective in precipitating solsare the same which are most adsorbed .

When adsorption of salts takes place by livingcells or by colloids , the electric state of the colloidis very frequently of great influence on the processof adsorption . Most of the organic colloids are

,

as was shown above , negatively electric . Theymust consequently act like acid anions , andwill in adsorption chiefly attract the bases of thesalts . I f the salt is in a highly di luted statepractically adsorption only of ions can take place .

Mainly the cations , viz . the metal ions , are re

fained by adsorption , while the anions remain to acertain extent unaffected . Hence

,of course , must

result reactions of acids , without any chemicalproduction of acids . Doubtless such adsorptionphenomena are of great interest for physiology .

I t has for a long time been well known that rootsof plants produce the effect of acids upon the soil

$0


and its constituents . It is possible to Show thisby letting roots grow along polished marble plates .After some weeks the marble surface clearlydemonstrates the dissolving effect of growingroots and root - hairs . Delicate traces are everywhere etched in the marble surface , where rootshave come into close contact with the plate . Iwas able to show , in 1 894, that carbonic acid iscertainly to a great extent responsible for thisphenomenon . I made plates o f plaster of Parismixed with di fferent substances , the solubility ofwhich in water saturated with carbonic acid

,

had been well considered . I discovered thatonly such compounds are dissolved by the plantroots and their excretion

,as were distinctly soluble

in carbonic acid . These were phosphate o fcalcium and strontium , but not aluminiumphosphate , which is dissoluble by carbonic acid .

Nevertheless,there are other effects of acids in

plant roots which cannot possibly be due tocarbonic acid , and which have not been explained until lately . Now it is believed to behighly probable that merely the adsorption effecttakes part in these phenomena

,and no excretion

of acids by the roots is to be assumed . I f the“ cations are adsorbed and anions of acids remainreactions of acids must result as well as in real excretion of acids . Now we can understand whyacids could not be discovered in the excre tiondrops of the root - hairs

,and why they react quiteSI


neutrally . Most probably even the acid propertiesof peat and of Humic Acids of the soil can beattributed to colloidal elective adsorption . Thenegatively electric colloids of the peat mossretain , as Baumann and Gully have lately shown ,chiefly the basic ions of the dissolved salts

,and thi s

adso rptive election must lead to reactions of acidin the soil extract . It can easily be demonstratedthat the citrate and the tartrate are most adsorbedand productive more o f the effect of an acid thanother salts of the same alkaline metal . I cannotbut suppose that the taking up of dissolved saltsby living cells is essentially founded upon phenomena of adsorption . This opinion has been confirmed by the chemical analysis of peat moss byBaumann and Gully . I t was found that thequantities of the basic mineral constituents of themoss - ash are almost the same as are adsorbedby the plant from the soil . Long ago agriculturalchemists had stated that the constitution of theash of plants which grow upon the same territorymay widely differ . This elective assimilation ofsoil constituents may be now explained to agreat extent by the adso rptive quali ties of thecolloids of the living cells .In summing up we may say that the super

ficial layer of cell protoplasm , called hy aloplasm ,

may be considered to be a film of more solid constitution which we call the plasmatic membrane .

This membrane regulates the change of substances52


in the metabolism of the cell , the assimilation offood taken up from outside the cell and theexcretion of substances from the cell . Theplasmatic membrane is not completely permeablefor all substances , but has a so - called semipermeable layer , which permits some substancesto pass through and others not . The protoplasmatic membrane is a compound colloid systemconsisting of an extremely fine fat emulsion sus

pended in a hydrosol,probably an albuminous

colloidal solution . We see , then , that fatty bodiesare taken up as well as watery solut ions . Con

cerning the latter , we are able to Show how important adsorption phenomena are in assimilatingthem . The laws of adsorption govern the assimilation of salts from the soil . Even the action ofacids can be produced by adsorp tive election .

80 we may say that a great many phenomenain life once attributed to Life Force

,and not to be

explained by chemical laws , can in the presentstage of science be reduced to the general Laws ofN ature .

53

CHAPTER V

CHEM ICAL PHENOMENA I N CYTOPLASMAND NUCLEUS OF L IVI NG CELLS

HE main body of protoplasm ,which is

surrounded by the hyalin layer of thesuperficial cell plasma , generally contains finelygranulated , slimy masses of a yellowish grey hue ,whence it is named Polioplasm. The appearanceof po lioplasm is very different according to the ageand the stage of li fe of the cells . Quite young cellsare found equally filled with homogeneous polioplasm . In the midst of this protoplasmatic massone perceives a spherical body of more solid condition which refracts light strongly : the N ucleus o/the cell. In the course of growth the polioplasmsoon produces drops of liquid contents in greateror smaller number . These drops increase in size ,and the polioplasm between them changes intothin lamellae separating the contiguous cavities .The po lioplasma gains the character of foam .

The cavities between the meshes of tough colloidmass are generally known as vacuoles . The furtherdevelopment shows the conflux of several neighbour vacuoles to one of larger size . The meshes of

S4



Distinctly the same effect is produced by theaction of salt solution . A flower stalk or leaf stalkof fleshy consistence put into potassium nitrateof about 2 per cent very soon becomes unelastic ,flexible , like a withered plant , and shortens itslength by some millimetres in a length of about1 0 centimetres . We learn from this phenomenonthat the pressing of protoplasm against the cellwall is due to osmotic forces . Hugo De Vriesshowed , in 1 884 , that it is possible to use thesuppression of osmotic pressure in cells or of theCell Turgor, as botanists say , by salt solution ,

for the measurement of the osmotic pressure innormal cells . The procedure is essentially identicalwith the so - called plasmolysis we have spoken ofin a previous chapter. One has to apply solutionsof a pure mineral salt of different concentrations .I t is usual to take potassium nitrate because it iseasily available in quite pure preparations andbecause the percentage in solutions is nearlyidentical with the standard gauge in chemicalwork , the Gramm M olecule Solution. Solution ofpotassium nitrate containing 10 1 gr . in 1 00 gr .water is only slightly more than 10 per cent concentration , and is a molecular solution , containingone gramm molecule potassium nitrate , 1 01 gr . in1 litre of water . I f we put sections of planttissue in different potassium nitrate solutions from00 5 normal to 0 2 normal strength , we find thatthe separating of the protoplasm from the walls

56

CYTOPLASM AND NUCLEUS

begins in solutions of about 0- 1 2 to 0 - 1 5 normalstrength . This salt concentration gives us agauge for the amount of turgor . De Vries showedthat all salts produce the same result at the sameconcentration in gramm molecules . We call suchsolutions which have the same osmotic effectI sosmotic Solutions . I f we are able to directlymeasure the osmotic pressure of one isosmoticsolution , for instance , of a sugar solution , by anosmometric contrivance , we may transfer thisvalue to the osmotic pressure in the cells . So it wasfound that the osmotic pressure in cells is equivalent to five and more atmospheres , one atmospherebeing equivalent to about 0 -

3 per cent of saltpetre .The action of polioplasma on the growth of

living cells consequently consists in the productionof substances which generate osmotic pressure .We know that only such substances as do not penetrate the protoplasmatic layer are capable of producing osmotic effects . I t is very little knownwhat substances having that effect are generallyproduced by plant cells . I t is seemingly highlycomplex acids related to sugar which participatein generating turgor effects in living cells . Introductory to the process of growth a certain amountof turgor pressure is ‘

indispensab le . We have toassume that by that pressure protoplasm as wellas the cell wall is thinned and first stretched

,then

new particles of cell wall substance are inserted,

57

CHEM ICAL PHENOMENA I N L IFE

by which process the expansion of the cell wallbecomes permanent .The most striking feature of

g

cell life is thefact that an enormous number of chemical reactions take place within the narrowest space .

Most plant cells do not exceed 0 - 1 to 0 -

5millimetres in diameter . Their greatest volumetherefore can only be an eighth of a cubic mi llimetre . N evertheless , in this minute space wenotice in every stage of cell life a considerablenumber of chemical reactions which are carried oncontemporaneously ,

without one disturbing theother in the slightest degree . How can we explainthis striking phenomenon In the first place wemust state that polioplasm is highly specialisedin its different parts . Besides the nucleus , whichcertainly is the seat of most important vitalactivities , we find many organs which are to berecognised with the aid of the microscope as

distinct protoplasmatic organs , and we alreadyknow the functions of many of them . Most plantcells contain clearly differentiated small bodies ofdifferent shape which are

'

employed in the serviceof the assimilation of sugar and carbohydrates .

In common plants they are green in colour , andpossess the remarkable power of absorbing carbondioxide

,if bright light is admitted , and of forming

sugar from the carbon dioxide and water . Theseare the chlorophyll bodies or Chloroplasts . Verylittle is as yet known about their detailed structure .

58


In my laboratory it was lately shown that the consistence of chloroplasts is often very soft , verymuch less solid than the nucleus . They con tain amixture of two kinds of colloids , one of them whichswells in water

,of hydroid character , the other

resembles fats and most probably contains thegreen colouring matter or Chlorophyll . In life ,as we may think

,the lipoid phase is distributed as a

very fine emulsion through the hydroid phase .

There are some other small bodies which are freefrom colouring matter

,and which form starch

from sugar . We call all these protoplasmaticorgans which are in the service of carbohydratemetabolism , Plastids . As far as we know , they arenever formed from other plasmatic parts . Theyalways take their origin from mother plastids bycleavage . In some plant cells there have beenfound special plasmatic bodies which form fat ,but more frequently fat is independently formedin the fundamental plasma substance . We maysay the same of the proteinsubstances of protoplasm . It may be , however , th at for the formationof all these compounds very small centres ordistinct organs exist , which cannot yet be recognised even by means of the highest microscopicalpower . In any case , the parts where the differentchemical changes take place must be separatedin some way from each other , to prevent mixingwith other substances . In colloid systems , as suchseparating walls , we find membranes formed of

59


precipitated solid colloids or gels . From the smallsize of these separated parts the whole protoplasmmust have the appearance of a foam formed bygel walls , inclosing in its meshes colloids of moreliquid state . This hypothesis is not withoutsupport from experiments . The eminent zoologistB iitschli , of Heidelberg , has shown for manycolloids , both inorganic and organic , that theyhave a foam - like structure which may be in somecases observed through the microscope . Evidentlysuch foam - like structure in protoplasm mustfacilitate the great variety of chemical processescarried on contemporaneously in the narrow fieldof a microscopical living cell .These structures can be transitory as well

as permanent . I t is very probable that in thecourse of evolution the former gave origin to thelatter . A problem of great interest is the questionof the nucleus . We know that the lowest organisms , such as Bacteria and the blue - green algaecalled Cyanophyceae , do not contain a typicalnucleus . In the Protozoa the nuclei are in manycases of much more primitive structure than inhigher animals . In the highly organised plantsand animals the structure of the nucleus is so

intricate , as is seen particularly in the processof the cleavage of nuclei , that the problem ofnuclear structure cannot be longer considereda chemical one . The nucleus rather acts as aspecial organism in the cell . To a certain

60


degree plastids may be spoken of in the sameway .

But the bulk of Cytoplasma shows clearly by itsvital phenomena that it is principally transitorystructures such as are found in other colloids

,

that Occur there . A wellknown fact is thestreaming of protoplasm . Streams of liquidcolloid matter wander in continual movementthrough the different parts of the cell , carryingwith them different bodies , very frequently thechloroplasts

,and in some cases even the nucleus

itself . Very little is known about the reason forthis remarkable phenomenon . The general impression is that surface tension plays a great partin such plasmatic streaming . By continual changeof the chemical properties of the plasmatic surfacephenomena may result such as are seen in streaming protoplasm . In any case , permanent structurecannot be given in freely streaming protoplasmwhich is continually moving in different partsof the cell . N evertheless , numerous chemicalchanges of the greatest importance must takeplace in the streaming polioplasma under thesame conditions which are found in other colloids .Just in this territory the chemistry of Li fe mayhope to obtain results of the widest significance .

6 1

CHAPTER VI

CHEM ICAL REACT IONS I N L IVINGMATTER

NE of the chief characteristics of living matteris found in the continuous range of chemical

reactions which take place between living cellsand their inorgan ic surroundings . Without ceasecertain substances are taken up and disappear inthe endless round of chemical reactions in thecell . Other substances which have been produced by the chemical reactions in living matterpass out of the cell and reappear in inorganicnature as waste products of the life process .

The whole complex of these chemical transformations is generally called M etabolism. Inorganicmatter contrasts strikingly with living substance .However long a crystal or a piece of metal is keptin observation , there is no change of the substance ,and the molecules remain the same and in thesame number . For living matter the continuouschange of substances is an indispensable conditionof existence . To stop the supply of food materialfor a certain time is sufficient to cause a seriouslesion of the li fe process or even the death of thecell . But the same happens when we hinder thepassing out of the products of chemical transforma

62



one of the chief tasks in explaining chemicalphenomena in life to study the different chemicalreactions which take place in living protoplasm .

Chemists working with li feless material haveas a rule to cause reactions by experiment

,since

the material does not undergo any change byitself . Comparatively few substances are readi lyaffected by the water and oxygen containedin the surrounding air

,without the help of the

experimenter . The biologist , on the contrary ,

may watch numerous chemical reactions whichtake place in living matter without his aid. I tis

,however

,difficult to study chemical reactions

in li fe in that way , because the single results cannotbe distingu ished or separated from each other .Results by far more exact are obtained when in anexperiment we bring together the living organismwith a certain substance to see what reactions arecaused . So we may watch the favourable orunfavourable influence of this substance on theliving cells as well as the chemical transformation ofthis substance by the living organism , when welater on subj ect the organism to chemical analysisor when we examine the products excreted by theliving cells . A great number of most valuableresults were obtained by such methods . Especiallythe gradual change of substances taken up intoliving cells by different reactions may be wellstudied in that way .

The next step is to learn what kind of chemical64

REACTIONS IN L IVING MATTER

means are available in living cells to produce suchresults . We have now to bring together the substance which we had examined in its reactions inliving cells with other substances in vitro . So wesee whether analogous influences may be exertedby some substances contained in cells or not .We compare the artificial reaction outside theorganism with the Vital reactions , and are enabledto draw conclusions from our experiment for thechemical reactions in living protoplasm . Strikingparallelism and resemblance are observed .

Such results , however , are incomplete , andhave been obtained only with certain groups ofsubstances . During the last decades biochemistshave more and more aimed at the study of thetotal complex of the living cell after its death inits reactions to certain substances . The earliestexperiments employed macerated tissue or wholecells of microbes under conditions which preventeddecomposition by living bacteria . Salkowskitwenty - five years ago allowed yeast to stand withwater and some chloroform , that he might studythe post -mortem transformation in this deposit ofcells . I t .was shown that many of the contentsof the living yeast cell undergo great changeunder such conditions

,and new substances were

found as products of such chemical reactions .Such chemical transformation in dead cells wheremicrobial decomposition is excluded , is calledAutolysis . Of late very ingenious autolytical

F 65


methods have been discovered . Instead of chloroform as an antiseptic toluol is generally used ,which liquid has scarcely any inj urious effectupon the substances of the cell . But , as Palladin ,

of St . Petersburg , has lately shown that even thegrinding down does harm to many vital reactions ,it is better to kill the living tissues by freezingand not to grind them . After having been frozenat 20 degrees , and having been placed in a glasswith some toluol , the organs are brought backinto room temperature . I t is said that under suchconditions more reaction takes place than whenthe material is ground down .

We owe to Edward Buchner, of Wurzburg ,another remarkable method which has the ad

vantage o i permitting us to work wi th liquidswithout any particles of living cells

,as in auto

lytical methods must otherwise always be done .

Buchner recommends the material being grounddown as finely as possible , and quartz sand orsilicious marl being added . The thick paste o fcells and silicious powder is then pressed out in anhydraulic press under a pressure of 300 to 500atmospheres . In this way all the cell sap isseparated from the solid parts of the cells

,and

contains but a very small quantity of cell fragments . Even these may be removed by filteringthrough a Chamberland candle filter . The clearcell sap , however , still contains many substanceswhich were hitherto known only in living intact

66

REACTIONS IN LIVING MATTER

cells . Macfadyan and Rowland proposed a verygood amendment of this method . The livingorgans are brought together with liquid air

,and

are very quickly frozen to stone - hard masses .Now they may easily be ground in the mortar .Before thawing toluol is added , and this paste ofcells is ready for autolytic experiments . Thesemethods

,highly developed as they are

,are con

tinually increasing in number and value . A considerab le number of reactions are now separablefrom general cell life , and these reactions may bestudied isolated from life . Such is the aim ofmodern biochemistry .

Chemical reactions are bound by certain conditions . They may by some means be acceleratedor diminished . The chief influences we meet within the chemical laboratory are temperature

,

physical condition , separating and mixing .

Chemists are always ready to boil a test whenthey desire to accelerate the dissolution or reactionof a substance . It is a matter of common knowledge that chemical reactions are considerablyhastened by a higher temperature . It is truethat plants as a rule do not Show a higher temperature than the temperature of the surrounding air .But there are remarkable exceptions . Bacteriahave been found in rotting hay and other decomposing plant material and also fungi , which produce a very high degree of heat even as muchas 60 degrees . Similar results were obtained with

67


leaves which were kept in a chest carefully isolatedto prevent loss of warmth . We may consider thatheat is generally produced by plants , j ust in thesame way as by warm - blooded vertebrates . Butthere are no contrivances in plants to keep thetemperature at a certain point above the temperature level of their surroundings . From numerousexperiments we learn that plants are in their vitalfunctions adapted to a certain average temperature . Not a few tropical plants suffer from frostand even die when the outside temperature fallsbelow four degrees above zero . At the sametemperature

,on the other hand , many alpine

and arctic plants have to perform all their functionsin life . In tropical plants the fat of the seeds meltsas a rule at a temperature of 30 to 40 degrees . It issolid at the ordinary room temperature of 1 5degrees . European plants always Show the meltingpoint of their fat not far above zero . Dailyobservation teaches us that plant li fe developsconsiderably more quickly in a higher temperature .

Growth , respiration , and the assimilation of carbondioxide

,as well as the phenomena of movement

and stimulation,reach a much higher velocity

and power in a temperature of 30 to 35 degreesthan in one below 20,

and by far higher than in atemperature below 10 degrees .The eminent Dutch chemist Jacobus HendricusVan ’

t Hoff discovered the rule that chemicalreactions are influenced by temperature with the

68

REACTIONS IN LIVING MATTER

result that the velocity of reaction is doubled ortrebled when the temperature increases by 1 0

degrees . This rule,well known to the chemists

of our days as Van ’

t Hofi’

s Rule or the R.G .T.

Rule, is in practice applicable between the extremes of 50 and 300 degrees . Below and abovethese extremes the quotient is larger than 3 orsmaller than 2 . It is of great interest to see thatchemical reactions in plants strictly follow thesame rule . F. F. Blackman and Miss Mattheeishowed that the dependence of the carbonassimilation of leaves in sunlight upon the temperature is an exact example of Van

’

t Hoff ’s Rule .

Blackman stated the same for the respiration ofplants . Kanitz drew attention to many formerobservations of different authors which demonstrate quite sufficiently that theR.G .T.

- Rule is available for protoplasma - streaming

,geotropism

,longi

tudinalgrowth , pulsation of vacuoles in cells , etc .As well as the influence of temperature onchemical reactions

,the influence of the physical

condition of the reacting substances is an oldlaboratory experience : Corpora non agunt nisi

fluida . The chemist is accustomed to dissolvethe substance which is to be used in an experimentto react on other substances . The chemical coursein living cells is the same . All substancesdestinedfor reactions are first dissolved . No compound istaken up into living cells before it has been dissolved . So the mineral salts of soil

,the organic

69


compounds when be ing digested by the leaves ofDrosera or by parasitic fungi are dissolved beforethey enter further chemical reactions in the livingcells . Digesting is essentially identical with dissolving , or bringing into a liquid state . On theother hand , the chemist knows how to save asubstance from chemical change by reactions , bytransferring it from the state of solution into asolid state . This is what is called precipitation .

The solid insoluble depo sit of the substance nowremains chemically unchanged . Metabolism inplants employs the same means . Substanceswhich are to be stored up

,such as starch , fat ,

or protein bodies,are deposited in insoluble solid

form , ready to be dissolved and used wheneverwanted for the life process . Further substanceswhich are useless or even poisonous are easilywithdrawn from the complex of chemical reactionsin living protoplasm

,and form a solid insoluble

deposit . For instance,oxalic acid is a wide

spread product of oxidation in living cells whichhas strong poisonous properties . Oxalic acidimmediately forms an insoluble compound whencalcium salts are present . In reality deposits ofoxalate of calcium are most common in plantcells . We may then maintain that oxalic acidis in this way withdrawn from active metabolism .

Resins and essential oils in quite a similar mannerare isolated and separated from the other react ingsubstances in living protoplasm .

70


CHAPTER VII

VELOC ITY OF REACT IONS IN L IVI NG CELLS

HEMICAL reactions are very frequentlypractically completed at the same moment

at - which they begin . I t is quite impossible tomeasure the time which elapses from the momentwhen the reacting substances are brought incontact up to the moment when the end of thereaction is reached . When solutions of nitrateof silver and of sodium chloride are mixed , thetwo solutions immediately form the well - knownwhite

,flaky precipitate , and , provided that there

is enough nitrate of silver present, all the chlorine

is deposited in the fo rm of insoluble silver sal t .Most reactions used in analyt ic Chemistry arereactions of enormously great velocity . Wecomprehend , therefore , why chemists did not turntheir attention to the laws of Reaction Velocitytill in the last decades , when organic synthesiscontinually taught that there are many chemicalreactions which require a considerable length oftime before being ended .

Most reactions in Inorganic Chemistry takeplace between electrolytes— substances which aregood conductors of electric currents . Many

72

VELOC ITY OF REACTIONS

reasons are brought forward in favour of a Viewwhich Faraday had first expressed , to explainthe conducting of electric currents . The moleculesof electrolytes are split

,to a greater or less extent ,

into smaller particles which are called I ons .

These ions carry the electricity from one pole tothe other . They may be considered , as physicistsbelieve , to be compounded of atoms and a certainquantity of electricity . The number of moleculessplit into ions depends upon the degree of dilutionand the temperature . Strong acids and alkalisare practically entirely split up into ions whenthey are diluted down to 0 -001 of one grammmolecule in one litre of water .The reactions which such substances undergo

may be considered as reactions between ions .We generally call them I onic Reactions . We shallbear in mind that ionic reactions are carried outwith infinitely great veloci ty . The quantity o fions contained in a solution can be calculatedby determining its power of conducting electriccurrents . The less resistance is offered the moreions are present . The sap of living tissues alwayscontains different ions . Therefore ionic reactionsmust always take place in living protoplasm .

Ionic reactions in living cells did not fail toattract much attention amongst biologists . Wepossess a series of excellent methods for determining the concentration o i ions contained inliving cells . Some of them permit us to work with

73


extremely small quantities of material . Especi

ally useful are the cryoscopic methods which allowus to determine the number of ions in the volumeunit from the depression of the freezing - point incomparison with that of pure water . The chiefsource of ions for plants is the moisture ofthe soil taken up by the roots . It contains ,in a very di luted state , salts of sodium , potas

sium , lime , magnesium iron , also hydrochloric ,sulphuric and phosphori c acid . Practically onlyions of t hese substances pass into the livingplan t cells . Some of these ions must disappear in reactions very quickly . Thus inliving cells we cannot find potassium in the wellknown reactions with platinum chloride . Tracesof potassium salts immediately furnish the yellowdeposit of platinum potassium chloride , but thisresult cannot possibly be obtained in living cells .When we burn the tissue to ashes and try thereaction again , success is certain . We maydraw the conclusion that potassium salts are probably transformed in living cells into non - ioniccompounds of potassium .

Very important is the formation of ComplexI ons in metabolism. Iron salts

,for example

,are

certainly not present in living protoplasm , but thepresence of iron is always easily shown in plantash . We can see what kind of transformationmay be taking place from the reaction of coppersulphate in the presence of organic compounds .


Sulphate of copper is immediately precipitated bypotassium hydroxide as a light blue gelatinous deposit of hydroxide of copper . When we add sugarsolution , or solution of sodium tartrate , this depositi s dissolved into a dark blue liquid . This liquid nolonger shows the characteristics of solutions whichcontain simple ionic copper . Therefore copperions cannot be present . Those present are compound ions containing both copper and the organicsubstance .

Similar processes are , as we know commonin living cells . But living cells can even formnew ions from non - ionic substances . Whenoxalic acid is formed from sugar or proteinmatter , new ions of this strong acid come intoexistence . Many o ther cases of the product ionof ions from non - electrolytes in living cells couldbe mentioned . When reactions between ionstake place in protoplasm , they are not carried outin a watery liquid medium

,but in a colloidal

medium . I t is a question ,however

,whether the

Reaction Velocity is the same as in water . Ex

perimental work of the last years does not leaveany doubt that a colloidal medium diminishes thevelocity of chemical reactions as well as the diffusion of dissolved substances . Thus it is certainthat colloids of firmer consistence

,such as solid

gels , must retard the course of chemical reactions ,even of ions . In spite of this , ionic reactions arecompleted in an immeasurably short time , and

75


practically the influence of the Viscous colloidalmedium in protoplasm is of very little importancefor ionic reactions in living cells .The most important substances among thecarbon compounds of living matter are notelectrolytes . N either sugar , fatty bodies , carbohydrates , nor protein bodies conduct the electriccurrent but to a very slight extent . All thesesubstances , then , which form the greater mass ofliving protoplasm are non - electrolytes , and inwatery solution will only form a very smallquantity of ions or no ions at all. Most of thechemical reactions which take place in assimilation ,digestion , and excretion are connected with suchnon - electrolyte organic compounds . It is, therefore ,of interest to learn how great the velocity of suchreactions is in comparison with ionic reactions .It is very eas ily Shown that reactions betweenmolecular solutions are carried out comparativelySlowly , especially when the temperature does notexceed 20 degrees . So it is when starch is transformed into sugar , or protein into amino - acids ,that there is no difficulty in measuring the velocityof chemical reactions . Such experimental work isvery important to obtain an exact theory of thedifferent chemical processes in living protoplasm .

We define as Reaction Velocity the quantity of thesubstance transformed

,measured in gramm mole

cules per litre,which disappears in the unit of

time , viz . in one minute . I f there is only one76


substance transformed at the same time in themixture of reacting substances , and if , therefore ,the concentration of only this substance varies ,whilst the other substances remain unchanged ,themathematical law of the process is quite simplyfound . The velocity of such a reaction mustdirectly depend throughout the reaction on theacting quantity of the substance . Since thisacting quantity of the substance is constantly decreasing

,we see that the velocity of the reaction

cannot remain the same . I t must diminish in acertain ratio . Suppose 20 parts out of 1 00 aretransformed in the first minute , then there remainin the second minute only 80 parts

I OO— I OOX 0 -2=8o .

We find for the process in the third minute thesame

80— 80x 0 -2=64

In the fourth minute64— 64 >< o

-2 , etc .

When we introduce for 100,which is the concentra

tion at the beginning of the reaction,the general

symbo l C0,and for 80, 64 , 5 1

-2 , etc . , subsequentlyC1 ,C2 ,C3 , C and for the constant factor

02 the symbol k,the equations are

C0- C0k=C1 or CO ( 1—k) =C1

furtherC0 (1— k)— C0k (1— k)=C2

OT Co ( I — k)2=6 2

77


furtherC0 ( 1—k)

3=C3

CO

I f,instead of 1 , we take the time unit equal towe have to take k n - times smal ler , and , in

stead of t,to write nt. The equation will now be

Co (1—9 =C

I f we introduce for f the value 5, we have forn=kd. The equation then becomes

Co

The expression ( 1 can be developedaccording to the binomial theorem into e

,the

basis of natural logarithms . The equation can beformed as follows

COX e"=C

Or i f we take logarithmsln C

O— ln C,

=kt.

By introducing Brigg ’s logarithms we haveki =o

-

4343k=% (log Co—log C.)

This expression contains values which may bedetermined by experiment . I f we therefore findthat the quotient of the difference of the logarithmsin the beginning and at the end of the time ofobservation , measuring the time in minutes , isconstant , we may be certain that only the con

78



Such reactions are called Bimolecular Reactionsor Reactions of the Second Order. Many reactionsin living cells follow the law of these reactions .Reactions o f a higher order are not as yet knownfrom living cells . We may at least be certainthat the great maj ority of all reactions in livingmatter are not connected with the chemicalchange of more than two di fferent substances .In molecular reactions we generally meet with

the peculiarity that the reaction is not quite com

pleted when the reaction velocity has reached thevalue of O. A certain quantity of the originalsubstance always remains and never disappears .Molecular reactions are consequently incomplete .Thus a small quantity of cane sugar remains unchanged when cane sugar is split by means ofdiluted hydrochloric acid , and in the same waysome quantity of the unsplit ester remains when wesplit it by means of acid into alcohol and acid .

This remarkable phenomenon becomes quite cleari f we suppose that the two reactions always takeplace in opposite directions . Simultaneously withsplitting up begins the synthetical reaction , andsynthesis increases in propOit ion as the splittingof the compound advances . The velocity of thesplitting process decreases at the same rate as thevelocity of the recomposing process increases .At a certain time both processes have the samevelocity . No further change takes place in thechemical system , provided that nothing is taken

80


away nor added . The characteristic stage ofequilibrium of the reaction has been reached .

We express this rule by writing the chemicalequation connected by a double arrow instead ofthe Sign of equation

c,H,OH CH3COOH 21

> C2H500C-CH3

—l- H20

E thyl alcoho l Acet ic acidZ Ethyl acetate Water

or C6H 12O6+C6H1206 Z C12H22011+H2O

Glucose Fructose Z Saccharose Water

This theory involves the condition that all thesereactions may be reversed under certain circumstances . It only depends upon the external conditions in which direction the situat ion of thestage of equilibrium is displaced , either"in thedirection of composition or in the direction ofdecomposit ion . We may draw the further conelusion that many chemical processes in living cellsmay obey this kind of law . Under certain circumstances cells may contain more grape sugar andfructose , under other circumstances more canesugar . Only chemical or physical agents influencethis relation , and we need no longer take refugein mysterious Vital forces when we want toexplain these facts . Just such chemical reactioncomplexes occur most frequently in living cells .The digestion and dissolution of organic matter inthe cell on the one hand , and the storage of organicmatter on the other

,must be ruled by analogous

G 81


laws . When there is a scarcity of food , the digestion of starch or protein must yet be continueduntil the concentration of the disintegrat ionproducts has reached a decisive point . Buthas the concentration risen above a certain point ,the process of recomposition becomes predominant ,with the result that storage of starch or proteintakes place .Such regularity can only exist as long as no

reaction products are taken away or added . Whenwe remove the products of dissimilation

,e .g . the

sugar produced in the decomposition of starch,

the splitting process continues and does not ceaseuntil the whole stock of starch has disappearedand has been transformed into sugar . Workingupon this principle we can deprive seeds entirelyof starch

,even the isolated endosperm when the

embryo has been removed . The seeds are fastenedeach upon a small cylinder made of plaster ofParis , which is placed in a dish filled with water .The principle of such an experiment is quite thesame as that which is followed in the emptyingof leaves of starch during the night . In the processof respiration and growth at night the growingplant consumes considerable quantities of sugar .At the end of a warm summer day leaves are fullo f starch , and allow a constant stream of sugarsolution to be directed to the places where sugaris consumed . By this process the decompositionof starch grains is continually assisted , since all

82


the sugar which has been formed from starch isimmediately removed .

The contrary effect, V iz . that further formation

of compounds is hindered when the s torage of thiscompound has reached a certain stage , is also afrequent phenomenon in living organisms . Whenleaves are cut off from the branch and are exposedto sunlight under favourable conditions of life ,for a certain time they continue their assimilationof carbon dioxide

,and starch is formed to a con

siderab le extent . Even more starch is stored insuch leaves than in normal leaves which have notbeen separated from the plant . But , after a time ,carbon dioxide assimilation diminishes and ceasesentirely . The concentration of sugar in the leafcells becomes too great and the assimilation processis hindered by the reaction products .The mechanism accelerating and ceasing re

actions in living cells is very often simply regulatedby the general laws of reaction velocity

,and we

need not assume any special power of living protoplasm . The next chapter will touch on one of themost important influences on the reaction velocity

,

and will show that living cells possess most effectivemeans to accelerate reactions and to cause sur

prising chemical results .

33

CHAPTER V III


N the beginning of the last century chemi stsmade the acquaintance of a series of re

markable phenomena , which were caused byfinely divided metals , particularly by platinum inthe form of the so - called P latinum black. Amixture of oxygen and hydrogen immediatelyexplodes when it is brought in contact withplatinum black . Common coal gas inflames whenbrought in contact with finely divided platinum .

Sulphur dioxide is by the same agency quicklyoxidised to sulphuric acid . Hydroperoxide israpidly split into oxygen and water when incontact with platinum black . In all these casesthe quantity of platinum black is not diminishedafter the reaction . an the products of the reactionsare never any of the platinum compounds . Similareffects were later on known from sulphuric acidin its influence on the formation of ethyl etheror sulphuric ether from the common ethyl alcohol .Here

,too

,no sulphuric compound is formed .

Ether is often called Sulphuric Ether for thereason that it is prepared by means of sulphuric

84


C H

C2Hz

> O does not contain

any sulphur . It is formed from alcohol Simply byloss of water 2 (C2H5

OH ) O.

No sulphuric acid is consumed in this process .Such remarkable reactions have become known incontinually increasing number . Since the effect ofthe metal or the sulphuric acid seems to be causedmerely by contact

,the German chemist Mitscher

lich proposed to call such effects Contact Eflects .

Mitscherlich recognised a very important fac tin many of such contact reactions , Viz . that inthese the large surface of finely divided contactsubstances must play an important part . Thefamous Swedish chemist Berzelius , who took agreat interest in these phenomena , believed that apeculiar force is exerted by contact substances .He called that force Catalytic Power. The nameCatalysis has since been generally accepted . Catalytic reactions soon became most important forbiology. Just a century ago Kirchhoff

,of St .

Petersburg , found that starch is transformed intogrape sugar by the working of mineral acids .It was known to him that no acid is consumed inthis process . In 1 833 Payen and Persoz in Parismade the discovery

,which has had far - reaching

consequences , that germinating seeds contain apeculiar contact substance , which transformsstarch into sugar . This substance they namedDiastase. In quick succession similar reaction

85

acid . Its formula


effects were recognised in the formation of prussicacid from the so - called amygdaline in germinatingbitter almonds

,in the formation of the sharp

essential oil in germinating mustard seed , and ,finally , in protein digestion in the stomach of manand the higher animals . Berzelius did not hesitateto express his opinion that catalytic reactionswill probably one day represent the most important part of the chemistry of living cells .At present , indeed , we have at our disposal asurprisingly great mass of facts which illustratethe general occurrence of catalytic substances inliving cells and the overwhelming importance ofcatalytic reactions for chemical phenomena in life .

I shall try to explain the position of our knowledgein the following pages as well as it is possible todo in a narrow space .

To Ostwald , of Leipzig , we owe a very ingeniousand practical defin ition of catalytic reactions andcatalytic power. Substances which act as Catalysers , as we now call them ,

usually exert theirinfluence upon a suitable substance , even whenapplied in very small quantities . As a rule onepart of the effective substance may transformmany thousands , even millions of parts of thesubstance undergoing the catalytic change . Butduring the reaction the quantity of the catalyserdoe s not diminish . For instance , when splittingup cane sugar into glucose and fructose by meansof acid , the acidity of the solution does not Show



effect as proportional to the quantity of thecatalysing substance . So the acceleration of thesplitting of cane sugar by acids was found to bedirectly proportional to the concentration ofthe acid applied . Another difference is shown bythe experience that release effects in processesof stimulation in plants or in animals do not occurwithout a stimulus . But catalytic reactions , asit seems

,are not strictly dependent for their

existence on the presence of the catalyser. For aseries of reactions it has already been statedthat the reaction takes place even without thecatalyser being present , yet , it must be admitted ,Slowly .

We come to the conclusion that the catalysingsubstance is only an accelerating agent

,but not

an agent without which the effect does not takeplace at all . This is very important for an exactunderstanding of catalysis effects . I f we findit desirable to compare the catalyser with any

mechanism in an engine , we cannot compare itwith a releasing contrivance

,but we may rather

find a resemblance between the effect of train - oil onthe smooth going of the engine and the acceleratingeffect of a catalysing substance .H itherto only accelerating catalysis has been

spoken of. Some effects on chemical reactionshave been found which seem to have the contraryof an accelerating catalytic influence . The oxi

dation of sulphurous acid , for example , can be88


very much retarded by traces o f glycerin , mannitol ,or other organic compounds . The luminosity ofphosphorus is diminished or hindered by thepresence of turpentine , ether, or alcohol . Probably all such influences are based in the workingof these agencies on a catalysing substance . Inthe first case which we have mentioned

,traces of

copper contained in the common distilled waterof our laboratories exert a catalysing influenceupon the oxidation of the sulphite of sodium .

Organic substances,for example mannitol and

glycerin , are inclined to form compounds of copperand so they remove the effective catalyt ic agentfrom the water , and diminish the velocity of theoxidation of the sulphite of sodiumWe owe to Bredig , ofZurich , the exact knowledgeof the retarding influence of traces of prussic acid

,

sulphide of hydrogen and some other substanceson the catalytic reaction of platinum black andhydrogen peroxide . There is no doubt thatprussic acid or hydrogen sulphide change thesurface of the platinum , for they cover it with alayer of platinum cyanide or sulphide . So theplatinum surface which exercises the catalyticpower is very considerably diminished . Bydecomposition of the cyanide layer the pure platinum surface can be restored and the catalyserbecomes active again . There is an interestingparallelism between these phenomena and thepoisoning of living cells by cyanide or sulphide

,

89


which made Bredig call such retarding substancesPoisons for catalytic and enzyme efiects .

A very interesting result in chemical reactionsis often given by the phenomenon that the catalysing substance is formed by the reaction itself.Pure copper metal is very much less soluble inquite pure nitric acid than in nitric acid whichcontains a little nitrous acid . The latter acid hasa catalytic influence on the process of the dissolvingof copper . Now some small quantity of nitrousacid is always formed by the reduction of thenitric acid during the process of dissolving copper .We therefore see that , after a certain time , thecopper dissolves much more quickly than in thebeginning . Such a catalysis is calledAutocatalysis .

We may compare it to the influence of heat on thedissolution of sodium hydroxide , during whichprocess heat can be produced by the process itself.Catalytic substances sometimes , in the same way

as platinum black or acids,may influence a large

number of reactions . Acids particularly are quiteusual catalytic substances which affect nearlyevery kind of reaction .

It is a very important fact that the final equil ibrium in the reaction is as little altered by thepresence of the catalysing substance as that theorder of the reaction is changed . Consequentlythe catalytic influence does not extend but to thereaction velocity . Catalytic reactions are of thegreatest importance for chemical phenomena in

90



believed , and that it was the active cause of thefermenting . From that time yeast has been placedin the plant system among the fungi . A little laterRutzing was able to show that the cause of aceticfermentation was also a microscopic plant , b elonging to the bacteria . It is still well rememberedwhat great services Louis Pasteur rendered to theknowledge of microbes which cause differentfermentations . In consequence of these discoveries the name of ferments was transferred tothe microbes causing fermentation . I havealready taken the opportunity of mentioning afurther wonderful discovery of the remarkablethird decade of the last century . I mean theisolation from germinating seeds of a substancewhich is able to transform starch into sugar .Payen and Persoz first showed that extract ofmalt contained a certain substance

,soluble in

water , and which was precipitated by alcohol ,which causes the starch grains to dissolve andinduces the formation of sugar from starch . Thetwo French scientists even showed that this substance , to which was given the name of Diastase,immediately loses its power when boiled . Theodore Schwann , at about the same time , discoveredthat from the mucous membrane of the stomachthere can be extracted a substance which is solublein water or glycerine

,and which acts very effec

tively upon albuminous compounds , quite in thesame way as in digestion the living organ changes

92

CATALYSIS AND THE ENZYMES

albumin . This substance was called Pepsin.

In rapid sequence followed the discovery ofEmulsin,

which splits up the amygdalin containedin almonds to prussic acid , benzaldehyde andgrape sugar the discovery of Myrosin in mustardseeds

,which produces mustard oil later on the

discovery of I nvertin in yeast , which cane sugarsplits into its sugar components Trypsin in thepancreas gland of quadrupeds , which rapidlySplits up albumin to amino - acids . Many otherdiscoveries were made later on

,in connection

with which I only mention the importan t statement of Schoenb ein in Basel , that oxidising effectsare caused by substances which are soluble inwater

,precipitated by alcohol and destroyed by

boiling . All these"

substances exercise theiractivity , even when applied in very small quantities . They are all of organic origin , never foundin inorganic nature , and not to be gained bychemical synthesis . We do not wonder that sucheffects caused by diastase and the other sub

stances mentioned were not sharply distinguishedfrom the microbial processes of fermentation ordecomposition . We indeed see the expressionF ermentation used for both kinds of phenomena .

I t was found sufficient to speak of Soluble Fermenisand ofM icrobic F ermenis .

Kuhne , of Heidelberg , was the first to propose tochange the nomenclature and to avoid speaking offerments . He clearly recognised that even the

9 3


microbes cannot act other wise but by productionof substances which must be regarded as So lubleFerments . Consequently the name of Enzymeswas introduced for soluble ferments . We knowthat all enzymatic processes depend upon theproduction of such substances . All the processeswhich were formerly believed to be exclusivelyconnected with living protoplasm are due tosubstances of the group of Enzymes .

In this direction,particularly the discovery of

Edward Buchner, of Wiirzb urg , then in Munich ,

was of the greatest importance . I t was shownin 1 894 that the power of fermenting sugar in yeastis by no means inseparably connected with cell - li fe .

When yeast is carefully ground down, so that

every cell is sure to be cut through or squeezed ,

and afterwards the paste is pressed by means of apowerful hydraulic press

,a yellowish liquid is

obtained which still possesses the full propertyof forming alcohol and carbon dioxide from grapesugar . Buchner succeeded by filtration in freeingthis liquid from every trace of living cells or theirfragments , so that there could not be any doubtthat no living protoplasm was present . Further ,he demonstrated that the alcohol - forming agentwas soluble in water

,precipitable by alcohol , and

very easily destroyed by heat . So alcoholicfermentation was separated from yeast - life andthe perspective was Opened

,that many other

processes of decompo sition or disintegration of

94



tinctly that every cell contains such enzymeswhich are not to be extracted from protoplasm ,

and which never diffuse from intact living cells .Such enzymes were named I ntracellular Enzymesor Endo- Enzymes. Other enzymes , such as thecane sugar inverting enzyme of yeast , or thedigestive enzyme of the mucous membrane of thestomach are abundantly secreted and conse

quently may be obtained without difficulty inany quantity from living tissue . These are theenzymes which we call Secretion Enzymes .

We understand that chemists were very anxiousto iso late pure enzymes and to study the propert ies of these most remarkable substances inthe hope of being able to explain why they act inthat way . In spite of the very advanced technicalachievements of experimental chemistry , it wasnot possible to prepare a pure enzyme

,not even

in one case . The difli culties of preparation arevery great . All enzymes have proved to betypically colloidal substances , and they readi lyShow alterations o f their properties , coagulate ,are destroyed by heat

,Show a high degree of

adsorption of other substances,and are mixed

with very many similar colloidal substances , sothat the chemist , in his endeavour to separatethe effective agent from its companions , losesmore of it the longer he treats it with reagents ,and often finally has before him a white powder ,looking quite satisfactorily pure

,but of much

96


less activity than the original enzyme . We mustconfess that it is at present impossible to sayWhether all enzymes belong to t he class of al

b uminous substances , as in many cases seemsprobable

,or whether enzymes may be of different

chemical structure . It is not even certain whetherall enzymes contain nitrogen .

As far as we know all enzymes are distinctlycolloidal substances . No enzyme survives boilingeven for a short time . Although there is greatuncertainty about the chemical nature andrelation of enzymes we possess much knowledgeof the action of enzymes

,which is doubtless the

most interesting part of the1r characteristics .At the first glance we must feel reminded ofcatalytic reactions . Berzelius made no differencebetween enzymes and catalytic substances . Aswell as being catalysers the enzymes Show strongactions even when applied in but very smallquantities . It Was stated with regard to a seriesof enzyme reactions that the quantity of theenzyme is not diminished in a perceptible degreeduring the reaction . We know further that theenzyme never appears among the products of areact ion , quite as in catalytic reactions . Finally ,it is most probable that the reactions which arecaused by enzymes do not entirely depend for theirexistence upon the presence of the enzyme . Theyare continued and take place , though very slowly ,even when the enzyme is not present . We see that

H 97


the chief characteristics of catalytic substances andof enzymes agree exactly. Wemust in consequenceof this consider enzymes to be catalytic agents .But there are a few very remarkable and sharp

differences between the two groups of substances .Most of the catalysers we have spoken aboutextend their sphere of action over a large numberof substances . Acids

,for example , are able to

catalyse all kinds of reactions . Quite a differentbehaviour is met with in enzymes . As a ruleenzymes are effective only in one reaction . Invertin does not act upon anything else but oncane sugar

,emulsin only upon amygdalin . Their

sphere is,as we see , very limited . Another peen

liarity of enzymes is their colloidal nature and theirinability to resist boiling temperature . There islittle doubt that both properties are connected

,

and that the sensibility to heat is due to coagulation of colloidal solutions . We may therefore saythat enzymes are catalytic substances of a limitedfield of action , of colloidal nature , and very littleresistent to heat . We must still add that enzymesare formed only in living matter . Finally , oneimportant property of enzymes is this

,that in the

blood of animals which have had some enzymesolution inj ected into a vein

,peculiar substances

are formed . These have the power of hinderingthe enzyme action when a little of the blood serumis added to a mixture of the original enzymesolution and the substance on which the enzyme

98



as well as albuminous bodies it acts on oxidisablesubstances and splits up fats . The same wasfound of paste formed from animal liver . Mostprobably a large number of different enzymesoccur in the narrow space of each cell . I t isastonishing to see how all these actions can beexerted at the same time without disturbing eachother and how exactly regulated they are . Wehave here another argument for the subtle strueture which protoplasm must possess

,that every

substance of the cell is kept in its proper place,

and cannot mix with the others . I t is an important fact that enzymes of a certain kind arenot formed by the organism under all conditions .That was Shown distinctly in experiments onmoulds . The common mould , Penicillium glaucum,

when cultivated on starchy material produces inabundance an enzyme which acts on starch ,

theso - called Amylase or Diastase. But if the fungusis kept on starch - free food , it has been found thati t does not contain any diastatic enzyme . Thelatter is only immediately and abundantly produced when starch is added to the culture medium .

Penicillium even produces an enzyme which actson wood subs tance , as I once showed . But such anenzyme is only produced if the fungus is cultivatedon wood and not upon any other substance . Wemust conclude that the formation of enzymes inthe organism underlies some regulations

,and that

it is a purposive process in life .

N ow comes the question What enzymes maybe formed of . Very little has hitherto been discovered about the origin o f enzymes . Only a fewhints are given by a series of experimental results .In a number of

'

cases it has been stated thatextracts from cells do not contain ready andeffective enzymes . But when they are treatedwith very diluted acetic acid or other milderchemical agents they begin to Show distinctworking on fat or albuminous matter or on starch .

Therefore the supposition was arrived at that thefresh cell - extract contained the natural mothersubstance of these enzymes

,and that this mother

substance was able to furnish the enzyme itselfby artificial transformation . The original sub

stances were called Pro- Enzymes or Zymogens .

Studies on'

the pancreat ic ferment in animalintestines have shown that the fresh pancreaticj uice does not act on protein bodies . But when itis brought together with the intestinal liquid itbegins to act most energetically on proteins . Theintestinal liquid entirely loses its activating effectwhen boiled . The activating substance mus tconsequently be destroyed by heat q uite asenzymes are . Other experiments showed thatthe activating substance of the intestinal sapmuch resembles a true enzyme

,and it may be

called an Enzyme activating Enzyme, or K inase.

Enzyme effects are assisted also by many othersubstances . We know the great influence which

10 1


is exercised on the protein - splitting enzymeof the stomach - secretion by hydrochloric acid oranother acid in sufficient concentration . Many ofthe enzymes of plant cells are favourably influencedin their action by acids quite in the same way .

The pancreatic enzyme on the other hand showsa contrary behaviour . I t is suppo rted by dilutedalkaline solutions . Very remarkable is the

activating effect on the fat - splitting enzyme of thepancreatic gland exerted by the organic acidsof bile , the glycocholic and taurocholic acid .

Such activating effects are extremely widelyspread in the part which enzymes play in the lifeprocess . One sees how these enzyme effects maybe regulated , strengthened , and weakened , as

the effects are required .

Many chemical substances hinder enzymereactions in a most characteristic manner . Strongeracids or stronger alkalis generally diminish theenzyme effects as also alcohol , formaldehyde ,cyanide of potassium

,aromatic substances , and

many inorganic substances , such as the salts ofheavy metals

,iodine

,sulphurous acid , etc . Such

a paralysing influence is not only exercised bythese substances

,but the living cell is able to

produce special substances,which a re destroyed

by heat,which are effective in very small quanti

ties , and which paralyse enzyme reactions . Wehave spoken of these already as the Anti - Enzymes .

Anti - enzymes are doubtless produced in theI 02



disintegration of the enzyme . The higher thetemperature the more unstable are enzymes .At a temperature of over 60 degrees enzymes arerapidly decomposed , many become immediatelyinactive when they are heated up to 63 to 65 degreesCelsius . We therefore understand that thereprobably exists a certain temperature at whichthe enzyme work is best done , viz . one at which theaccelerating effect of the temperature is strongenough to finish the reaction very quickly , andwhere the enzyme destroying effect of the tem

perature is not so strong as to paralyse the tem

perature effect on the velocity of the reaction .

This relation can be shown graphically by twocurves . The line AB shows the acceleration ofthe enzyme reaction by the rising temperature .

We take it for granted that this influence is directlyproportional to the temperature . The curve CDshows the destruction of the enzyme by thetemperature rising . This influence as far as weknow is not simply proportional to the temperature .

Suppose the quantity of the enzyme at o is 100,

and the quantity at 70 degrees is 0, we have todraw the curve CD. 50 we recognise that theoptimum of the effect lies between 50 and 60degrees . Only about 55 per cent is active , butthe strong acceleration of the reaction velocityneutralises this diminution . At 60 degrees about

40 per cent of the enzyme is active . Consequently ,this minus is to be subtracted from the ordinate ,

104


and the resulting curve of the enzyme effectSlightly approaches the axis of abscissas . At ahigher temperature the quantity of the activeenzyme decreases rapidly

,and so does the re

sulting effect , which becomes 0 at 70 degrees .

A 10 20 350 4 0 60 00 70

Such superposi tion of two curves causes theculmination of the resulting curve in E . In praetice it is not advi sable to use too high a temperaturefor enzyme reactions . A medium temperature isin most cases the best . We Shall not be surprisedto see that this so - called Optimum of enzymereactions coincides with the temperature whichis most favourable for the life process . FLFrostBlackman , in a series of most interesting papers ,showed that the dependence of different life

105


processes on the temperature obeys a similarrule to that of enzyme reactions . Whenever wefind an Optimum of a certain vital function at acertain temperature we must think of the crossingof two kinds of influences . One of these influences is the accelerating effect of the temperature on chemical reactions , the other thedestructive effect of higher temperature on theactive substances of living cells . We only haveto add that most of these active substances belongto the enzymes .It is important that the equilibrium of Enzyme

reactions is not altered by temperature . Van ’

t

Hoff has explained this fact . Enzyme reactionscause neither a great production nor a great consumption of heat . All reactions of such character ,of a comparatively small caloric change are notaffected in their equilibrium by temperature .

Therefore the constant of equilibrium in enzymereactions is not dependent on temperature .

Bright sunlight is very harmful for enzymes ,and rays of light destroy them very quickly .

Especially the ultraviolet rays act particularly injuriously on al l enzymes hitherto examined .

Very interesting relations exist between the concentration of the enzyme solution and the enzymeeffect . We have related that many catalyticreactions follow the law of monomolecular reac

tions . So ,for example

,the destruction of hydrogen

peroxide by platinum so", or the splitting up of cane106



If k is the constant of the reaction velocity, x the

transformed albumin,M the not yet decomposed

albumin , then the equation can be written as k

x -

,M or M : k

l

( 1According to the rule of Schutz

,the ratio of the

transformed albumin x to the time wanted for thetransformation is

x=k1 IN or x2=kf- t

differentiate , we find

dx k"1

2x - dx=k;- dl or

dl 2 x

As long as M is proportional to the reactionvelocity ( 1 ) Schutz

’ rule must therefore be valid .

Another question is whether even enzymereactions are of the first order , that is , are monomolecular reactions or not . We see that thequestion is of great importance . In the case of theenzyme reaction being really of the first order , weknow that only one substance in its concentrationis altered during the reaction . And that cannotbe any other than the substance on which theenzyme is acting . Consequently the enzyme concentration itself remains constant . In this way weobtain the proof for the identity of enzyme re

actions and catalytic reactions . As early as 1 890excellent papers were published by O’

Sullivan andThompson on the reaction between cane sugarand invertase . These authors came to the conclu

108


sion that the reaction follows the law ofmonomolecular react ions . This theory was by no meansgenerally accepted . French and German scientistsof great weight denied that the law of the reactionis simply the law of mass effect , and empiricformulas were calculated which sufficiently agreedwith the course of reaction observed . It is toHudson that we owe the proof that O’

Sullivan

and his collaborator were quite right . Theable American chemist found that the chiefmistakes in such investigations are caused by thecircumstance that grape sugar continually changesits action on polarised light when just split offfrom cane sugar . This property of glucose iscalled mutarotation . Hudson very cleverlyavo idedthis source of error by adding some alkali to thesolution before the polarimetric determinationwas made . Thus the state o f equilibrium is at oncereached in the rotation and the determinationsof glucose can be made without any diffi cultyand with full certainty . In this way it was clearlyshown that the inversion of cane—sugar by invertaseis just as much a monomolecular reaction as theparallel reaction of cane - sugar inversion by meansof acid . Investigations were made on fat - splittingenzymes which showed the same law , but theresults of others were different . But anotherenzyme very clearly follows the law mentionedabove . That is the catalase

,which splits up

hydrogen into water and oxygen . Finally the109


tyrosin oxidising enzyme of plant cells wasfound to follow the law of monomolecular re

actions . Even ii we do not yet possess clearknowledge about other important enzyme re

actions,these results are most remarkable . Hope

is given us that some more enzyme reactions arequite identical in their mechanism with catalyticmonomolecular reactions . Since we have seenthat Schutz ’ Rule can be simply explained

,and is

by no means peculiar to enzyme reactions,we

believe that it is very probable that enzymes arenothing else but organic catalytic substanceswithout any peculiar property . Complications

,

it is true , are frequently produced by the colloidalpropert ies of enzymes , which cause the greatinstability of the enzymes . In most cases thequantity of the enzyme is diminished at the endof the reaction because of the destruction of acertain amount of enzyme in other reactionswhich occur besides the main reaction . I t iseasily understood that this must lead to importantdifferences from the law of monomolecular re

actions .Finally we have to touch on the question of the

specific character of the different enzymes . Apriori we do not know whether one and the sameenzyme cannot catalyse different reactions . Butmany reasons can be given for the suppositionthat by far the greater number of the enzymesact upon only one substance . Al though most

I IO



Then amylases have been met with which didnot Show this guaiacum reaction . Finally extractswere obtained from plants which only gave theguaiacum reaction but did not act upon starch .

So the conviction was arrived at that the bluereaction with guaiacum and the starch - decom

posing effect belong to different enzymes,which

,

it is true,very often occur together .

Since we know very little about enzymes ,except of their action ,

it is natural to found thesystem of the enzymes upon the kind o f reactionwhich each carries out . Thus the nomenclature ofenzymes nowadays is generally taken from theenzyme action . It was found convenient tocompo se the name of the enzyme with the ending- ase, taken from the first desc ribed and isolatedenzyme

,the Diastase. As the root of the name

of an enzyme,is taken the name of the substance

which is decomposed by this enzyme . So weshall call starch - decomposing enzymes , fromamylum,

starch,Amylase ; similarly the enzyme

acting on cane sugar Saccharase, etc .

The chemical characteristic of the enzymereaction or the special decomposition caused bythe enzyme is very di fferent . In many , cases theaction consists

,as in cane - sugar inversion or

starch dissolution,merely in an addition of water ,

which is followed by a splitting up of the substance .

Chemists generally call such effects Hydrolysis.

All enzymes which provoke hydrolysis may be


united in the chemical group of HydrolyticEnzymesor Hydrolases . Among these enzymes di fferentsub - orders may be distinguished according to thechemical order to which the substance attackedbelongs . If esters or compound ethers of alcoholsand acids are decomposed by enzymes the lattermay be called Esterases ; if they act on carbohydrates , Carbohydrases ; if they act on fats ,Lipases , etc .Other enzymes have the peculiarity that they

split off the group NH2from nitrogen containing

organic substance . Since this group is called theAmido - group , the enzymes must b e namedAmidases . To such enzymes belong even themost important enzymes which act on proteids

,

the Proteases . Certain enzymes produce precipitations in albuminou

‘

s solutions by hydrolysis . Wecall them Coagulases .

Another group is characterised by the oxidisingeffects of its enzymes . These are the Oxidases .

Their counterpart is formed by the Reductases , orreducing enzymes . Further are known enzymes ,which split off carbonic acid from organic acids .We call them Carboxylases . Perhaps even theenzyme which causes the alcoholic fermentationby yeast , the Zymase, belongs to these .

For physiologists it is ra ther more interesting todistribute the enzymes according to their physiological significance in the living cell . Followingthe physiological principle , we may distingu ish

1 1 13


three large groups of enzymes : enzymes in theservice of the assimilation of food and of digestion

,

enzymes employed in respiration,and those

employed in dissimilating processes partly formingthe so - called end - products of metabolism . Wemay maintain that all decomposing processesconnected with the assimilation of food are ruled byenzyme reactions . The end of all these reactionsis to form from the substances occurring in foodthe primitive stem - substance

,such as glucose

from the carbohydrates or amino - acids fromalbuminous substances . Each cell contains suchenzymes

,and is able to reconstruct its substances

from the fundamental organic groups which areformed from the food by a host of enzyme reactions . In consequence of this , each cell is ableto rebuild its own specific albumin from the food

,

and does not take up the albuminous substancesas they are present in the food without any change .

We therefore distinguish two stages in the digestionand assimilation of foo d . One stage is merelyanalytical

,a splitting stage . Here the different

hydrolytic enzymes,such as lipases , amylase ,

saccharase,maltase

,the proteases , develop their

"

activity . In the following stage the reconstructionof cell - substance takes place

,the synthesis of

the organic principles of life . Modern chemistryhas been fortunate enough to obtain even hereremarkable results from experiments .We should remember that hydrolytic processes

1 14



of yeast , there are formed grape sugar and a compound which is a combination of glucose and thenitrile of amygdalic acid . Concentrated solutionsof glucose and the nitrile - glucoside broughttogether with emulsin form in abundanceamygdalin , the original glucosid of almonds , a sO. Emmerling has shown . Undoubtedly synthetic effects were further observed

,when lipase ,

the fat - decomposing enzyme,acted on a con

centrated mixture of glycerine and fatty acids .Finally some synthetic effects are known fromthe enzyme which act on proteids . All these ex

periences render it very probable that the organicsynthesis in cells is performed and regulated byenzymes

,and we can no longer consider the

formerly mysterious synthesis of organic compounds in life as a problem which is not accessibleto chemical experimental investigation .

No less important prospects lie disclosed atpresent relative to the part of enzymes in theprocess of respiration . It was Lavoisier whoclearly recognised that the respiration of animalswas a process analogous to inorganic combustion .

About 1 800 Saussure , of Geneva , during hismemorable investigations into plant nutritiondiscovered the respiration of plants . Since thattime no doubt has existed that the fundamentallaws of the process of respiration are the samein both the plant and the animal kingdom . It istrue that in plants and in the lower animals one

1 16


characteristic is missing which most manifestlydirects our attention to respiration as a process ofcombustion . It is the development of free caloricenergy . But it is not difficult to Show by means ofsuitable contrivances that each plant produces anabundant quantity of heat in respiration . Weonly have to keep germinating seeds in a Dewarglass for several days to show that the temperaturein the glass rises to 40 degrees and more . Carefulisolation therefore is sufficient to demonstratethis production of heat . Physiological investigation taught that in both animals and plants thematerials of combustion are essentially the same .Most frequently large quantities of fat , sugar , orcarbohydrates disappear during the process o frespiration . The striking feature in such chemicalprocesses in life is that these substances are notused to produce new cell - substances

,but in the

first place to furnish free energy,which is used to

maintain the life - processes .The growth and the amount of respira tion in afungus or in germinating seeds show what greatquantities of carbon dioxide are produced in a Shorttime , and how much sugar is consumed in respiration . When we try to compare this vital decomposition of sugar with the sugar - decomposingprocesses which we apply in the laboratory

,we

shall find it astonishing what effects are producedin living cells without any high temperature

,any

strong chemical reagent or electric current . A

1 1 7


lump of sugar may be exposed to the air for yearswithout showing more alteration than that it turnsslightly yellow . Thus we come to the conclusionthat organisms must possess special means whichproduce the rapid decomposition of respirationmaterial .The chemist Schoenb ein,

of Basel,was the first

to show that enzyme - like substances take part invital oxidation . He drew attention to the propertyof many plant tissues of turning a colourless emulsion of resin of guaiacum in water blue . He thenshowed that the effect on the guaiacum resin isalso found in the filtered watery extract of thetissue

,and that this oxidising effect cannot possibly

be obtained if the extract be boiled beforehand .

Later on numerous substances were found to besuch oxidising ferments . All plant and animalcells contain such enzymes . But they act only onaromatic substances

,as phenols and resin acids

on sugar or on fat they do not show any effect .The explanation of this fact came from thediscovery that pea - seeds

,which are brought to

germination without access of air , produce a largequantity of alcohol besides carbon dioxide . Thisprocess

,which is found widely spread in plants

which are kept without oxygen from the air ,proved to be fully identical with the alcoholicfermentation of yeast . Even the enzyme whichBuchner had found in yeast and had called zymasewas stated to be present in higher plants . We

1 18



as with oxygen,and with some bacteria it is

the same . For other microbes the presenceof air is deleterious

,as they soon die when

brought in contact with a medium containingeven only small quantities of oxygen . Thepossibility of life without oxygen can be shownby the following experiment . A flask is filledwith a culture medium of sugar

,pepton , and

Lieb ig’

s extract of meat . This liquid is sterilisedby boiling and infected with bacteria from teguments of bean - seeds . A quantity of solubleindigo is added to stain the liquid dark blue .

Then the flask is well corked and allowed to remainfor one or two days in the incubator at 25 to 30degrees Celsius . After this time we are sure tosee the liquid quite colourless , the soluble indigobe ing reduced by the anaerobic bacteria whichdevelop rapidly and take the oxygen from theindigo . When the bottle is reopened and its contents poured slowly out into a dish

,we see the

liquid immediately colouring greenish , then lightblue , and soon dark blue , as it was before . Thischange is brought about by the reabsorption ofoxygen from the air . Such experiments showdi stinctly that bacteria can grow without morethan minute traces of oxygen , and that undersuch conditions the bacteria are able to drawoxygen from its compounds by reduction . Differentresults that have been arrived at lead to the conelusion that enzymes also take part in this process

120


of reduction . These so - called Reductases seemto be widely spread in lower and in higher plants .Finally

,we have to report that enzymes take

part in the formation of such products of metab olism as are no longer of any use for the organism .

They are removed from it as excretions , or formin the tissue deposits which do not change . Inanimal life a great quantity of nitrogenous substances are eliminated from the organism , as ureaand uric acid . It has been shown by severalauthors that enzymes participate when theseexcretion substances are formed . When thebacteria which cause putrefaction of meat arepreparing their cell - substances from the pro teins ,a number of atom - groups from protein are eliminated as waste substances . Particularly whenputrefaction is going on without sufficient accessof air , many substances are formed which areresponsible for the peculiar smell o f putrid matter ,and which are to be considered as bacterial excretions . Such are some compounds of sulphur

,

hydrogen sulphide itself , and methyl - mercaptanfurther , indol and scatol are substances which arevery characteristic of putridity . No less must aseries of phenols be mentioned as products ofputrefaction . We have certain proofs for the Viewthat all these substances take their origin frOmamino - acids , which are the primary products o fthe decomposition of proteids . By splitting ofcarbon dioxide and of ammonia the formation of

IZI


the substances mentioned above is easily explained ,and it becomes more and more probable thatenzyme reactions can cause these decompositions .In the case of some of these enzyme reactions wemay be sure that they even occur in the cells ofhigher plants and animals

,and are not confined

to the lower organisms .After our short review of the immensely extended territory o f catalytic and enzymaticphenomena in the living cell

,we cannot but confess

that the importance of such processes is surprisinglygreat . The large number of different chemicalreactions which take place in living protoplasm ,

and which we know from physiology to be thefundaments of chemical phenomena in life , iscomparatively well understood at present on thebasis of enzyme - chemistry .

It is true , there are some most important chemical processes in living cells which do not yetform part of catalytic chemistry . I may heremention the unique synthetical process in plants ,the formation of sugar from the carbonic acid ofthe air by the chlorophyll bodies of green cells insunlight . But any day may bring the revelationthat even here catalytic phenomena are at work ,and nothing at present excludes the suppo sitionthat enzyme effects take part also in these phenomena of plant life . I f we suppress our feelingsof satisfaction that Exact Science has been ableto penetrate into these mysteries of life , there are

1 2 2



life as in inanimate matter . In inanimate Nature ,further , we always meet with the importantphenomenon that caloric energy can never betransferred from a colder body to a warmer one ,unless other Special processes render it possible.By itself heat can only be transferred from awarmer to a colder body . This law ,

well known inLord Kelvin ’s utterance

,that the energy present

in the world has the tendency to dissipate , doubtless governs living matter as well as non - living .

There is only one part of physiology which is notyet accessible to our methods and which we cannotprove to be ruled by the well - known laws ofinanimate Nature . These are the psychologicalphenomena . At present we see no way to transferphysical and chemical methods to the phenomenaof the psychical world.

CHAPTER IX

CHEM ICAL ACT IONS ON PROTOPLASMAND ITS COUNTER- ACT IONS

ITHERTO we know living protoplasm as acomplicated system of colloidal substances

possessing a highly developed structure,and ruled

by a great number of catalytic reactions . Thecomplex of these reactions is able to maintain thecell - structure

,to take up substances from outside

the cell to digest them and to gain from themboth energy and cell - substance for growth .

We have not yet completely treated of themutual chemical interchange between the outerworld and living cells . This influence consists insomething more than in taking up food and givingoff excretion substances . The whole life - processdepends to an enormous extent upon externalchemical influences . Minute traces of iron salts

,

scarcely to be ascertained by chemical analysis,

possess the power of greatly accelerating grow thand respiration . Life can be destroyed by othersubstances in quantities which are infinitelysmaller than the mass of protoplasm which thedeadly substance can injure . Such influences

1 2 5


may be called Chemical Stimuli . Their action isquite comparable to the action on living matterof physical stimuli , such as light , warmth ,

electricity and gravity .

6 I t is quite a general rule that substances whichproduce poisonous effects on living cells whenapplied in a certain concentration , influence livingcells quite differently when their concentration ismore diluted . Then stimulating effects areregularly produced . Respiration and growthreach a higher degree than without applicationof the poison . For example , potato plants treatedwith copper sulphate show darker green leavesand more vigorous stems than normal plants .We see that poisonous action does not dependonly on the chemical nature of substances

,but also

on the concentration of the substance . We shouldrather speak of poisonous effects than of poisonoussubstances . The explanation of the phenomenamay be given by the principle of action and counteraction . The poison— for example , mercury chlorideor carbo lic acid— develops a retarding influence onsome processes in living protoplasm . Protoplasmis by this action incited to react against theinjuring influence . This is done by an accelerationof the chief processes of life— respiration

,growth

,

and probably many others . So the toxic influence is paralysed . The successful counter - actionagainst the poisonous agent cannot , however ,take place when the toxic influence is too strong .

126



actions are observed in living protoplasm wheno ther cells and their products , not only an inorganicpoison , are the inj uring part . We may be remindedof the interesting phenomenon with which webecame acquainted in the formation of antienzymes . In the animal which has had an enzymesolution inj ected into its veins

,a substance is

formed which is able to hinder the action of thisbut of no other enzyme . Such phenomena arewidely spread and are most important for thestudy of chemical processes in cells . In studies onpathogenic bacteria it has been shown that manyof them produce substances which are mostpoisonous even in the smallest quantity , but di fferfrom other poisons by their albuminoid characterand their instability when heated . By boiling theymay be easily destroyed . Such poisons are formedonly by living cells . We call them Cytotoxins .

Such cytotoxins have become known not onlyfrom bacteria

,but even from higher plants and

animals . The fly - agaric and some of its relations ,the seed of the castor oil plant and of Croton ,

as well as the seed of Abrus precatorius , theJequirity plant

,contain toxins of exceedingly

strong action . Cytotoxins,further

,are found in

snakes,toads

,the blood of the eel and some other

fish . I f we consider the characteristics of cytotoxins we feel very much reminded of the properties o f enzymes . The resemblance increases whenwe learn that cytotoxins

,quite in the same way as

1 28

CHEM ICAL ACTIONS : PROTOPLASM

the enzymes , cause the formation of specific antisubstances when brought into the veins . Theformation of Antitoxins is quite analogous to theformation of anti - enzymes . Antitoxins have thespecific effect of rendering the Cytotoxin , to whichthey correspond

,ineflicacious . This Antitoxin

phenomenon , as we know , plays an importantpart in the defence of animal and human organismsagainst the toxin - producing bacteria in infectiousdiseases .The production of anti - bodies is a most remark

able feature in the mutual chemical influencingof living cells against alien living cells and theirchemical products . Especially for pathology

,the

study of such phenomena is at present of thegreatest importance . A whole new branch ofbiochemistry , called Immunochemistry, has beenbuilt up upon the basis of the general experiencesmentioned above .

In our general review of the chemical phenomenain life we cannot but lightly touch on the factswhich Show how the living organism protects itselfagainst the attacks of microbes . These facts arevery interesting for us to illustrate how the protective substances and the aggressive substancesof living cells may enter upon reactions . Cytotoxins , as well as enzymes , are typically colloidalsubstances , and so are antitoxins . When antitoxins neutralise the cytotoxins we could thinkthat the cytotoxins would be destroyed . But it is

K 129


not so . I f we heat the mixture of antitoxin andcytotoxin to nearly the temperature at which thelatter is destroyed by heat

,we can reach a point

where the mixture again becomes toxic . Weget the impression that the antitoxin in the compound has been sooner destroyed by heat than thecytotoxin , and the latter has again become free andeffective . This most important experiment showsus that both anti - substances enter into a combination , analogous to that of chemical compounds .Since we know that bo th substances are colloids

,

we could suppose that colloid reactions are re

sponsible for the phenomenon . Otherwi se wecould think that the reaction is to be considered achemical combination of both substances . Atpresent there are many difficulties in the way ofgiving a satisfactory explanation of the reaction .

Arrhenius drew a most instructive parallel betweenthe neutralisation of toxin and antitoxin

,and the

neutralisation of a moderately strong alkali , such asammonia

,with a weak acid

, e .g . boric acid . Bothprocesses

,indeed

,have a great resemblance .

Ehrlich ’s ingenious hypothesis , well known as theso - called Side Cha in- Theory, cu lminates in thesupposition that the anti - substances representhighly compound molecules with many atomgroups

,such as proteids possess . The neutralisa

tion is done by binding two di stinct groups . Thesegroups may be destroyed by heat , and both substances again set free . Possibly the two theories

130



obtained in albumoses and peptones,the most

primitive protein - bodies . There is every hope ofthe possibility of soon explaining this reactionmuch more exactly than is at present possible .

But even now we see what complicated reactionscan take place among proteids , and how easilyprecipitates are formed without seriously changingthe original proteids . Most remarkable is the factthat the proteids o f a species of plant or an imaldo not give any precipitin reaction with the bloodserum of an animal treated with the proteid of thesame plant or the same animal . Therefore thereaction can be used to distingu ish whether a proteid is an alien one , or one be longing to a certainspecies . Experiments were made by Uhlenhuthon anthropoid apes

,and on groups of lower apes .

Anthropoid serum from animals which weretreated with the blood of man does not give anyprecipitin reaction . But serum from other apeswhich were treated with the blood of man gives adistinct reaction . We see from this fact that theblood of anthropoids is not essentially differentfrom that of man . The proteids are the same inboth .

The result is that each species of organismhas its own specific proteids . We understandnow why the alien proteids which are taken inwith the food have to be split up until they finallyform amino - acids , so that the alien proteinstructure is quite annihilated . Then the cells

1 32

CHEM ICAL ACTIONS : PROTOPLASM

reconstruct the proteins according to the specificstructure of protein which is characteristic of thepart icular species of organism . Further, we learnfrom the experiments on precipitin reactions thatthe morphological po sition of a species in thesystem is also physiologically founded . We maysuppose that closely related species must alsoshow chemical relations . The chemical mechanismof the precipitin reaction is not yet clear . We canthink of the phenomenon mentioned in a foregoingchapter , that two colloids of contrary electriccharge flake each other out . Since albuminoussubstances readily change the kind of electriccharge , many opportunities would be givento cause such precipitate reactions . It has beenshown without doubt that the precipitin is entirelyconsumed in the reaction . Therefore we cannotstate that any resemblance exists with enzymereactions . Living cells can even produce specificsubstances having the properties o f proteidswhich have the power to agglutinate other cellsor unicellular organisms such as bacteria . Asimilar effect is obtained by adding to a cultureof typhoid bacteria in the test - tube some of theblood serum of an animal which had been previously treated with typhoid bacteria by in

travenous inj ection . Flakes of bacteria areformed , between them the liquid becomes quitelimpid , and the medium whi ch had been turbidwith bacteria shows itself later on quite clear , and

I 33


all the bacteria are found in the deposit . Thesubstance responsible for this reaction , the so

called Agglutination of Bacteria , is destroyed byheat and has the properties of a protein - body .

Substances of this kind we call Agglutinins . Eventhis reaction is a strictly specific one . Theagglutinin produced by inj ection of a certainspecies of bacteri a gives to the blood serum thespecific agglutinating action on these bacteria .

Agglutination effects occur even in other toxins .The toxin substance from the seeds of the cas toroil plant strongly agglutinates the red bloodcells , and so does the Jequi rity toxin . There is nodoubt that the agglutinin acts on certain substances in the bacteria - cells or other agglutinablecells . These substances are probably transformedinto a gelatinous state

,which is seen in the clinging

together of the cells . The agglut inin is entirely consumed in this reaction . It may therefore rather becompared to a neutralisation than to an enzymeaction .

The most successful study of the alterationswhich occur in the blood of animals , after intravenous inj ections of pathogenic bacteria andtheir products

,showed far more substances formed

which serve for the protection of the organismthan we have here mentioned . But al l thes esubstances

,such as opsonines , bacteriolys ins ,

and,further

,the bacterial substances , such as

aggressines and others which ass ist parasites


CHAPTER X

CHEM ICAL ADAPTAT ION AND I NHERITANCE

UR review of the chemical phenomena inlife would not be complete unless we had a

last glance at the chemical phenomena of variation ,

adaptation and inheritance in living beings . Theinvestigation of these phenomena lies at presentso much within the territory of morphologythat one scarcely thinks of the importance ofchemical work in this department of biologicalscience . Chemical methods

,however , are here

of particularly great interest . Morphology , being acomparative science , draws attention only to theresults of variation and adaptation . Chemistryhas to show the whole course of phenomena , notonly the results , and it has to consider the influenceof time on phenomena , to determine the minimaand maxima in the course of reactions , and tointroduce the Time Factor into all these in

vestigations . In chemistry , therefore , variationcan b e observed in the course of phenomena as wellas in the final results . Since alterations andvariations in the course of physiological actionscan generally be traced back to the influences of

136

CHEM ICAL VARIATION

certain factors , chemical methods open up animmensely wide outlook .

At present chemical investigations into variationand inheritance unfortunately show so many gapsthat our report cannot be but a provisional one ,and it must rather contain suggestion for freshexperimental work than material already workedout .The kinds of variations which morphologistsdistinguish as

'

F luctuating Variation and M utation

are exactly repeated in the chemical propertieso f living organisms . The Law of FluctuatingVariation discovered by Quetelet is expressedby the statement that the average values are themost frequently recurring ones . The individualsshowing a certain characteristic more or lessmarked , are rarer , the greater the divergence fromthe average value or average size of the characteristic . This law , which can so regularly beshown by measuring the length , weight or volumeof an organ of plants or animals in a great numberof individuals , supplies exact returns in chemicalvariations . De Vries gives a report of the resultof an examination of sugar beets withregard to their content of cane sugar . From thecurve given by De Vries we immediately recognise the fundamental law . The average quantityof about I 6 per cent of sugar was found in nearly

7000 beetroots ; 1 2 per cent sugar in only 340roots , 1 9 per cent in only 5 . It ~is true that such

I 37


research work has not been carried out very often ,

but the few experiments which have alreadyb een made render it most probable that Quetelet

’

s

law holds for chemical propert ies as well as formorphological characteristics . It would be com

paratively easy to examine the amount of acidcontained in leaves

,the amount of starch or of

protein which is contained in one individualin a great number of cases in order to confirmthe results mentioned above . No research workat all has b een done to determine the velocity ofchemical processes or reactions in a great numberof single individuals . Data without any di fficultycould be worked out on the veloc ity at which starchor protein disappear from germinating seeds or onthe intensity of respiration in many individualswhich live under exactly the same conditions . It isdifficult to say what results would be thus obtained .

In any case such research work is highly desirable .

The second kind of variation takes place sud

denly , eruption - like,and culminates in the pro

duction in single individuals of quite differentcharacteristics which are markedly inheritable .

Since De Vries ’ famous book on these phenomena ,we call such variations M utations . Chemicalmutations are widely spread and well known . Inhorticulture and agriculture many new mutationswhich were kept on account of their valuablechemical propert ies have in the course of timebeen isolated . Fruits , containing an extraordinary

r38



of this characteristic in the ancestors . There isno doubt that chemical atavism will frequentlybe found in connection with morphologicalatavism . We need only think of the reappearingcharacteristic of the uncultivated ancestors of ourfruit trees . But it is not yet known whether suchchemical atavisms can reappear without beingaccompanied by morphological atavism .

Finally , we have to turn our attention to thevariations which are caused by external influences .Botanists well know that the size and thickness ofleaves depend upon the intensity of the sunlightin which they have grown . Especially the intensity of light , but also the degree of moisturein the air , gravity , mechanical and chemica linfluences cause very remarkable al terations inthe morphological characteristics of plants . Atthe same time chemical al terations must takeplace , and we see at last from all the research workwhich has been carried out in that domain , thatthe variation is not merely a morphological one ,but is also chemical . One must feel it to be a gre atgap in biological work that chemical properties intheir dependence on the physical and chemicalinfluences of their surroundings have not yet beeninves tigated for themselves alone . But a numberof facts show even now that chemical variationdepends on the influence of environment , and thatit shows a similar purposive tendency towardsadaptation to the environment

,as is known in

CHEM ICAL ADAPTATION

morphological characteristics and variations . Theoil - seeds of the plants of the flora of our countryalways contain fat which is liquid at temperaturesof above I O to 20degrees Celsius , and becomes solidat a few degrees above zero . Tropical plants veryfrequently contain fat which melts only at atemperature above 30 degrees , and is solid at anaverage European temperature . This differenceis likely to be connected with the temperaturein which the plants live . Another phenomenonof the same kind is the rule in the production ofenzymes . In moulds no amylolytic enzyme isproduced unless these fungi grow on culturemedium conta1n1ng starch , and the common greygreen mould Penicillium glaucum produces anenzyme which destroys wood - substance

,when it

grows upon wood , but never when it grows onother substrata . For the formative action ofchemical and physical influences on the morphological qualities of organisms the term M orphoseshas been introduced . In an analogous mannerwe can name the chemical alterations provokedby these influences in plants and animals Chemoses .

Morphoses are to be considered as reactions of theliving organism to external stimuli . They belongto the physiology of stimuli , and we cannot butassume that they differ from tropisms and otherprimitive forms of reactions only in their com

plexity . Chemoses must be considered as reactionsof the living organism in the same way , and all

14 1


that is known about morphological reactions mustbe assigned to these reaction - phenomena .

Biologists are nowadays inclined to explain thephenomena of adaptation in plants and animalsby the supposition that the heredi tary adaptedforms took their origin from transitory morphoses ,which often do not last longer than the time duringwhich the external stimulus is acting on theorganism . In such a way may for instance beunderstood the origin of dorsiventrality in plants .A branch of ivy develops its rootlets only on theshade - side , and turns its leaves all to the sun- side .

I f we turn the branch by 1 80 degrees and fix itin this new position

,it changes its morphological

properties entirely , corresponding to the newconditions . The old rootlets shrink and fall , butnew climbing roots are formed on the side whichis now turned away from the light . The dorsiventrality is , as we see , not fixed . A branch of apine tree when turned by 180 degrees behavesquite differently . The old part does not changeits character

,and in spite of the unnatural position

the leavas remain without any reaction . Butwhen in the following spring the branch continuesits growth , the new part of the branch correspondsin its formation exactly to the new position . Wesee that a reaction could not be carried out in theadult part of the branch , but the characteristics ofthis part were not transferred to the new part .The latter behaves according to its real li fe con



since the progeny of bitter or sweet almonds,re

spect ively , invariably show their peculiar characteristic . Consequently the characteristic ofproducing amygdalin depends on the nuclei ofthe sexual cells . Generally , we speak of heredi tyonly when sexual processes are involved , and theproperties of one generation are transferred to thefollowing generations . In plants , however , it ispossible to take the conception of heredity in awider sense . Sensu stricto a sexual cell with itsproperties is a part of the parental organism whichis separated from the latter and is beginning anindependent life . For heredity I think we mus tnot lay too much stress upon this circumstance ,and it does not matter whether the transferring ofparental properties takes place among cells whichremain connected or not . When in a growingbranch the young part acquires its properties fromthe adult part

,this process is done by cell cleavage ,

each cell transferring its characteristics to itsdaughter - cells . We may consequently here alsospeak of phenomena of inheritance , and we shalldistinguish them as Asexual I nheritance. Theterm Inheritance implies that the transferring ofcharacteristics takes place continually from generation to generation . But it is not necessary for thecharacteristics to be apparent . Hybrids often donot show their characteristics in an intermediateform between the parental forms , but entirelyresemble in a certain respect one of their parents .

144

CHEM ICAL HERED ITY

Mendel showed that in the second generationthe hidden characteristic of the other parentbecomes manifest in 25 per cent of the descendants .So it must have been latent in the first generation .

Such cases of heredity we call DiscontinuousHeredity, continual manifestation of characteristicsContinuous Heredity.

Heredity is far from being an absolutely sharpand marked conception . Phenomena of typicalsexual inheritance are connected by an innumerable range of intermediate stages with the phenomena which we call typically transitory inductions . One could even think that Inheritancerepresents only the limit of longeval induction ,of which we cannot recognise the end , because theduration of our time of observation is too short.If we could follow up millions of generations

,i f we

could have the age of an eternal being , we mightfind the phenomena of variation more strikingthan the phenomena of inheritance . The bestmaterials with which it is possible to observe agreat number of generations in a few weeks aremicrobes and bacteria . There is one case knownwhich illustrates the conception of inheritancemost instructively . The Bacillus prodigiosas is amicrobe which , under normal conditions , is verynoteworthy because of its production of a scarletcolouring matter . When this bacterium is cultivated at a temperature of 30 to 35 degrees itgradually loses its colour. The interesting fact

L 145


is now that the property of being colourless remainswhen the microbe is again cultivated at theordinary temperature of 1 8 degrees . One wouldfeel inclined to suppose that it had lost its propertyof producing the red pigment by the influence ofheat . The loss is undoubtedly hereditary , formany generations are formed under normaltemperature conditions which are absolutelywithout any red hue . But after a certain numberof generations

,which may be many thousands , the

red hue returns,and the bacterium regains its

former appearance . Such phenomena seemto benot very rare . I f we were beings of quit shor tduration of life

,we would perhaps believe that the

loss of red pigment in these bacteria was realinheritance . Since we can prove that after a greatnumber of generat ions the former propertyreturns

,we call that P seudo - I nheritance. But

we must bear in mind that there is no sharpdistinction between pseudo - inheritance and realinheritance . The latter can only be consideredas a pseudo - inheritance which lasts for an infinitelygreat number of generations . Chemical phenomena in this territory will certainly be di scovered ,and perhaps will contribute much towards makingthese difficult questions clearer .Phylogenetic investigations still contain many

more interesting chemical questions than we couldtouch on in our short discussion . Well worthconsideration is the question whether the so - called

146


CHEM ICAL PHENOMENA I N L IFE

have essentially the chemical composition ofprotoplasm . In Ontology we see that the youngtissues of higher plants do not yet contain thedifferent chemical compounds whi ch are found inthe adult plants . Even here the chemical com

position of the cells is essenti ally thatof protoplasm .

INDEX

Adapta t ion , Chem ica l , 140Adso rpt ion , 49Agglut ina t ion ofBac teria, 134Agglut inins , 134Aggressins , 134Al coho l ic Fermen ta t ion , 94D

’

Alemb ert, 5Al ien Pro te ids, 132Amicrons, 26

Am i dases , 1 1 3Ana '

erob iosis , 1 19An t i - Enzymes, 99, 102Anti toxins, 129Arms trong, 1 15Ar rhenius, Sv. , 107, 1 30, 13 1

Atav ism , 139Autoca ta lysis , 90Auto lysis , 14 , 65

Bac terio lysins , 134Baumann , 52Berzel ius , 85 , 86 , 97B imo lecula r React ions , 80B iochem istry , 5Biogenet ica l Law, 147 D ias tase , 85 , 92B io logy, Compara t ive , 3 D io smosis, 45Experimen ta l , 4 Dum as

,8

B lackman , F . Fr. , 69 , 105Bredig , 24 , 30, 89Brucke, 1 1Buchner , E . , 66 , 94 , 1 18

Butschli, 60

Cagniard La tour, 9 1Carbohydrases , 1 1 3

L 2 149

Carboxylases , 1 13Ca talysis , 84Ca ta lyt i c Power , 85React ions , 87

Ca ta lysers , 86Ca tapho resis , 28Cavendish , 5Ce l l Turgo r , 56Chem ica l Reac t ions in L iv ingMa t ter , 62Chemo ses, 14 1Ch lo rophyl l , 59Ch lo roplas ts , 58Coagulases , 1 13Cohn , Ferd . , 1 2Co l lo ida l Proper t ies , 20Co l lo ids, 20Mo lecular Weigh t , 22

Physica l Proper ties, 22Con tac t Effec ts , 85Crys tal lo id S tage, 20Cy toplasm ,

13, 54Cy to toxins, 1 28

Ehr lich,1 30, 13 1

E lect ive Assim i la t io n of So i lCons t i tuents , 52Emmerl ing , O. , 1 16

Emulsin , 1 1 5Emulsions , 2 7Emul sion - Co l lo ids , 30

INDEX

Endo - Enzymes , 96Engine -Theo r ies ofLife , 14Enzymes , 19, 9 1 , 94Influence o f Tempera tureon, 103I n trace l lular

, 96

Syn theses by , 1 14Enz

‘yme Reac t ions , Optimum

o 105Es te rases , 1 13Etard , 18

Faraday , 2 1 , 73Fermen ta t ion , 9 1 , 93Ferments, 9 1So luble , 93

F isher , Em . , 9Foam S truc ture o f Pro toplasm ,

60, 7 1

Gels , 2 1 , 48Gibbs , W. , 4 1 , 43Goe the , 6Graham , Th. , 20, 2 1 , 22 , 32 ,

48

Gul ly, 52

Haeckel , 147Hales , St. , 4Hardy , 30He redi ty, Con tinuous , 145Disco n tinuous , 145

H i ll , A. Cr.

,1 1 5

Van ’ t Ho ff, 68, 106 , 1 15Van

’

t H ofl’

s Rule, 69 , 103Hofme ister , Fr. , 48, 50

Ho rmones , 1 27Hudson , 109Hum ic Acids, 52Hya loplasm , 34Hydro lases, 1 13

Hydro lysis , 1 1 2

Hydro ly tic Enzymes , 1 13

Immunochem is t ry , 129lngenhousz , 5Inher i tance , Chem ica l , 143Asexua l , 144

In ternal Secre t ion , 12 7Ionic Reac t ions, 73Ions , 2 1 , 73Complex, 74

I so smo tic So lut ions , 57

Kani tz, 69Ke lvin , 124K inases , 10 1K i rchho ff, K . , 85Kuhne , 1 1 , 93Kutzing, 92

M acfadyan and Row land , 66Ma ter ia l ism , 5 , 6Matthaei , M i ss , 69Mauper tuis , 5edium o fD ispe rsion , 29Mende l ’s Law,

139Metabo l i sm ,

62

Me ta l 8015 , 24M icrobic Fermen ts , 93

La Mettrie , 5Lavo isie r , 5 , 1 10Law o fN a ture , 2L ife , Engine -Theo r ies o f,Fo rce , 7Process of, 6S tufi Theo ries of, 15

L inder , 23

Lyoph i l Co l lo ids , 47Lyophobic Co l lo ids , 47


INDEX

S tuff-Theo r ies ofLife , 1 5Subm ic rons , 26O

'

Sullivan and Thompson ,108

Surface Tension of Pro toplasm . 4 1 , 43

Suspension - Co l lo ids , 29Suspens ions, 27

Tempera ture , Influence on

Chem ica l Reac t ions , 67Time Fac to r , 136Traube , 4 1 , 4 2Tyndal l ’ s Phenomenon , 24

Uhlenhuth , 132

Ultramicrosc0pe , 24

Var ia t ion , Chem ica l , 137F luc tua t ing , 137

Ve loc ity of Reac t ions , 72Vries

g, H . de , 36, 56 , S7 . 137 :

I 3

Woh ler , 8

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