Chemical phenomena in life

LIBRARY

OF THE

UNIVERSITY OF CALIFORNIA.

BIOLOGY

LIBRARY Class

G

HARPER'S LIBRARY of LIVING THOUGHT

CHEMICAL

PHENOMENA

IN LIFE

BY

FREDERICK
CZAPEK

HARPER
BROTHERS

LONDCNXNEWYOKK

CHEMICAL

PHENOMENA

IN LIFE

BY

FREDERICK CZAPEK

M.D., PH.D.' '

PROFESSOR OF PLANT PHYSIOLOGY
IN THE UNIVERSITY OF PRAGUE

HARPER & BROTHERS

LONDON AND NEW YORK

45 ALBEMARLE STREET, W.

1911

BIOLOGY

LIBRARY

G

Published September, 1911

PREFACE

IT has given me great pleasure to accept the
suggestion of the Editor of Harper's Library
of Living Thought, that I should treat in a volume
of this series some phases in the life processes of
plants.

There is scarcely any other question in the
biology of plants of greater interest than that
of the general chemistry of the cell, viz. of the
living protoplasm, which has been so successfully
worked at by the biochemists of our time. Not
only very important results, but also most sug-
gestive hypotheses, render this chapter of plant
Physiology more attractive than any other. The
molecular structure of living protoplasm, as well
as organic synthesis in cells and the hitherto
inexplicable phenomena of endosmosis in the cell,
have been rapidly placed in the foreground of
modern scientific problems and now range among
the great questions of biology to solve which is a
well-grounded hope.

So I could not resist the temptation to give a
short review of this territory of Biology which is so
full of suggestions and attractions. I was, however,

vii

228515

PREFACE

not unconscious of the difficulties met with in
laying all the questions mentioned above before a
wider circle of readers who have not devoted
themselves especially to physiological work in
biology. A fair knowledge of physics and chem-
istry, both organic and physical, is required
besides the great number of biological facts which
must be remembered when we try to obtain a
satisfactory survey of the general physiology of
the plant. It is therefore rather difficult to
present the subject of our book in a condensed
but clear and rather popular form, and I may
express my doubts as to whether it can be done
at the present day as perfectly as had been my
wish.

So I must beg my readers to be indulgent if my
intentions have not been carried out as I would
have desired. At least no one will finish the book
without the feeling of satisfaction that Modern
Science is going to touch on problems so lofty
that before our days their solution could never
have been dreamed of.

F. C.

UNIVERSITY OF PRAGUE,
Junt> 1911.

CONTENTS

CHAPTER PAGE

PREFACE . . vii

I, BIOLOGY AND CHEMISTRY . i

II. PROTOPLASM AND ITS CHEMICAL PROPER-
TIES . . 10

III. PROTOPLASM AND COLLOID-CHEMISTRY . 20

IV. THE OUTER PROTOPLASMATIC MEMBRANE

AND ITS CHEMICAL FUNCTIONS . . 35

V. CHEMICAL PHENOMENA IN CYTOPLASM AND

NUCLEUS OF LIVING CELLS . . 54

VI. CHEMICAL REACTIONS IN LIVING MATTER 62

VII. VELOCITY OF REACTIONS IN LIVING CELLS 72

VIII. CATALYSIS AND THE ENZYMES . . 84

IX. CHEMICAL ACTIONS ON PROTOPLASM AND

ITS COUNTER-ACTIONS . . 125

X. CHEMICAL ADAPTATION AND INHERITANCE 136

ix

CHEMICAL PHENOMENA
IN LIFE

CHAPTER I
BIOLOGY AND CHEMISTRY

THE establishing of the close connection of the
biological 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 of
the most important and most difficult steps taken
in the glorious era of the great French Encyclo-
paedists and Philosophers. Chemistry aims at
showing the diversity of matter. It tries to
separate 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 the
clouded path of the investigator and lead him up
to the heights from whence he has a clear and far-
reaching view over the silent fields of Nature.

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

CHEMICAL PHENOMENA IN LIFE

4 Laws " in Chemistry and Physics ? If the
conditions of a certain kind of experiment are
kept exactly the same, the experiment must in-
variably lead to the same result. Thus the same
result is shown, however often a physical or
chemical phenomenon of a certain kind is repeated
in Nature itself or by the hand of the experiment-
ing scientist. Single results, as they are produced
by arbitrary human action, vary. In a great
number of them we may already distinguish a
considerable number of average values. Suppose
this action is repeated infinitely often, mathematics
teach us that we may consider the average result
as the true and final value, and we may believe
this an equivalent of a Law of Nature. We see,
therefore, that Law in Chemistry and Physics
is the expression for the probability of the result
when a process repeats itself infinitely often.
Thus a phenomenon in Nature, such as the free
falling of bodies or the chemical reaction between
sodium chloride and nitrate of silver, may with the
greatest certainty be expected to take in every
case the same course which we have observed even
upon only one occasion. Chance and probability
are there excluded, and the full certainty of a
Law of Nature is given. Chemistry in consequence
may apply the means of mathematical calcula-
tion to the course, and the final results of chemical
change in matter. It belongs, as we say, to the
Exact Sciences.

BIOLOGY AND CHEMISTRY

Biology presents in every line a striking con-
trast to Chemistry. It does not need experi-
ments to such an extent as Chemistry does.
Chemical objects lie unchanged before us, their
qualities unaltered, unless we disturb them by
experiment. Animated Nature works upon our
senses in the most striking manner. In animals
and plants gay and bright colours delight our
eyes. How much too do we not feel attracted
by the different forms of movement in living
beings ? In the childhood of the civilisation of
mankind, as well as in that of the individual, Life
and Motion, without any visible external agency,
are nearly identical conceptions. The variability of
phenomena in animated Nature which are acces-
sible to mere observation without experiments
is so great, so infinitely great, that the method of
experiment in Biology seemed to be entirely
unnecessary to all great naturalists up to the
eighteenth century. Much more attention was
given to the comparison of the different phenomena
of life. This method is what we in our days call
Comparative Biology. This branch of Biology is
particularly occupied with the study of the form
and the structure of organisms, that is, Mor-
phology and its annexes, Embryology, Anatomy,
and Histology.

The more we feel the importance and pre-
ponderance of Morphology and of comparative
investigation in Biology, the more we must in-
3

CHEMICAL PHENOMENA IN LIFE

cline to the highest admiration for the genius
who first applied chemical and physical methods
to Biology. Stephen Hales' Statical Essays
(1727) are the memorial of the entrance of
Physiology into the ranks of the Exact Sciences.
These Essays contain the first application of
physical laws to biological problems. The pressure
of blood in the arteries and the pressure of sap
in the vessels of plants were henceforth facts ex-
pressed in exact mathematical values. In studying
Hales' Statical Essays we may most strikingly feel
the splendid progress in Biology which lies in the
application to the ever-changing living organism
of methods hitherto only applied to inanimate
matter. Experimental Biology entirely abstracts
from the qualities which to the naive eye of the
observer are characteristics of life. It enters the
territory of its investigation from the highest
philosophical point of view, that of the probable
connection of living and non-living matter.

Thus was built the bridge between Exact Science
and Biology. At present we may consider Ex-
perimental Biology an Exact Science as well as
Physics and Chemistry. All employ the same
methods, and their end is the same, viz. to lead
by means of mathematical conclusions to general
results which enable us to explain a greater complex
of facts starting from a limited number of experi-
mental results. I would prefer to speak of Ex-
perimental Biology rather than of Physiology, as is

BIOLOGY AND CHEMISTRY

usually done. The very experiment is what is
characteristic of the physiologist's method, in the
same way as comparison is the chief characteristic
of Morphology or Comparative Biology.

We shall not be surprised to first find physical
methods in predominance upon the field of Ex-
perimental Biology. This was in the age of Newton.
Some decades later the work of Lavoisier in France,
of Cavendish, Priestley, and Ingenhousz in England,
and of Scheele in Sweden brought the dawn of
scientific Chemistry. It was not a mere chance
that the discovery of oxygen was closely connected
with the important discovery of the fact that
living green plants produce in bright sunlight a
considerable amount of the newly discovered
gaseous element. We henceforth see Chemistry
and Physiology growing as sister- sciences, and no
era of Plant-Physiology was richer in important
discoveries than that of the foundation of modern
chemistry inaugurated by the great Lavoisier.
At the same time that Chemistry was born,
Biochemistry, or the knowledge of Chemical Phe-
nomena in Life, came into being.

Every extraordinary advance in Science was
accompanied by a revival of materialistic philo-
sophy. The age of Newton, Lavoisier, D'Alembert,
and Maupertuis was the mother of La Mettrie's
work L'Homme Machine. A century and a half
before our days imaginative minds even thought
of a chemical synthesis of living cells. When

CHEMICAL PHENOMENA IN LIFE

Goethe's poetical genius created Wagner, Faust's
famulus, mysteriously mixing hundreds of sub-
stances in his retort upon the chemical hearth,

" denn auf Mischung kommt es an,"

it was the reflection upon the great poet of myriads
of scientific phantasms of that time, as to whether
it were not within the reach of possibility to com-
pound Life itself from the elements which Chem-
istry had shown to be the pillars of the Universe,
and which were contained in every animate and
inanimate part of the visible world.

Again, further, the renaissance of Materialism
in the last century was the consequence of the
marvellous progress of Exact Science, which even
showed us the elementary structure of planets
and fixed stars, and taught us to construct in the
laboratory the vital compounds of animals and
plants, such as sugar, fat, and protein bodies, from
their very elements.

Here I need not give an extensive sketch of the
Natural Philosophy of our time in its relation to
Biology, and especially to Physiology. Only a
few remarks on the importance of experimental
physical and chemical methods in Biology may be
added. The enormous advance of our chemical
and physical knowledge of the life process may
easily lead to too far-reaching opinions on the
unique significance of these methods. Can Life be
explained by Physics and Chemistry ? Are our
6

BIOLOGY AND CHEMISTRY

methods in Biophysics and Biochemistry sufficient
to disclose the secrets of living cells and to unveil
the arcanum of Nature ?

Undoubtedly nearly all the exact physiologies 1
knowledge that we possess is based on physical
and chemical methods. Every year we are con-
fronted with new and surprising facts in the Physics
and Chemistry of animate Nature entirely parallel
to facts in the Physics and Chemistry of inanimate
Nature. But my conviction is that nevertheless
Physiology cannot be really identical with the
Chemistry and Physics of living organisms.
If we consider the explanation of the fundamental
problems of Life to be the aim of Physiology,
Physics and Chemistry will presumably not be
able to fulfil this great task for themselves alone.
It must, however, be conceded that it becomes
more and more improbable that Life develops
forces which are unknown in inanimate Nature.
Life force was said to produce the host of peculiar
substances which in Nature occur only in living
organisms, and are never produced by non-living
bodies. These substances were called organic
substances. The part of Chemistry which deals
with organic compounds is even nowadays known
as Organic Chemistry. The great Chemists of
France were the first to show that organic com-
pounds are for the greater part compounds of
carbon. The abundance of carbon compounds in
the animal and plant world, the scarcity of such

CHEMICAL PHENOMENA IN LIFE

compounds in non-living matter, form a striking
contrast. We are, then, not surprised to see that
at the beginning of the last century the view was
generally adopted that carbon compounds can only
be formed by synthesis in the living cell. To be
complete it must be mentioned that still in the
eighteenth century even the mineral salts in plants
were said to be formed in the plant cell by the Life
Process. Saussure, in 1804, was the first biologist
who proved unquestionably that all mineral salts
are taken up into the plant from their watery
solution in the soil, and that none are formed in the
plant itself.

In 1828 the question of carbon compounds in
living organisms was solved by the discovery of the
German chemist Woehler, that urea can be
artificially prepared in the laboratory from
ammonium cyanate. The deep impression pro-
duced upon the scientific world by this important
synthesis may be gathered from the opinion ex-
pressed by Dumas in 1836. The eminent chemist
stated that no sharp line of distinction could be
drawn between Inorganic and Organic Chemistry.
In plants and animals must rather dwell a peculiar
power of synthesis which it was henceforth the
task of Organic Chemistry to imitate. The
glorious range of organic syntheses during the last
century is still fresh in our recollection. Nearly
all the important animal and vegetable sub-
stances are at present accessible to artificial
8

BIOLOGY AND CHEMISTRY

synthesis from their very elements. Even protein
matter seems to have lost its mysteries since we
learned from Emil Fischer's work that amino-
acids can be combined in the same way as they
occur in protein. Compounds of amino-acids
can be obtained which show all the main reactions
of protein substances. Emil Fischer, of Berlin,
was the same chemist who in 1886 discovered how
to prepare grape sugar from glycerin. A con-
siderable number of plant alkaloids have been also
artificially prepared in the course of the last five
decades. The most important colouring matters of
plants, for instance, alizarin and indigotin, are no
longer extracted from plants for technical pur-
poses, but are accessible from the products of coal-
tar. We see, then, that animal and plant sub-
stances are by no means peculiar to the realm of
organic nature. They are compounded within the
living cell and without it by the same chemical
laws. Our task in experimental Biology can only
be this, to explore the material in the living cell
which carries out the chemical changes in sub-
stances, and to control the reactions which take
place in Life.

The following chapters try to show what success
has been attained in the endeavours of Science
in the bordering territories of Chemistry and
Biology.

CHAPTER II

PROTOPLASM AND ITS CHEMICAL
PROPERTIES

DURING its life and in the course of its evolu-
tion, the form of the body and its organs
is subjected to a continuous series of changes.
But at the same pace the organism of the in-
dividual undergoes chemical changes. Its general
composition is changed. Checnical analysis shows
new substances formed, which at an earlier age
were not yet present, whereas some substances
have disappeared. This is the parallelism of
morphological and chemical change in the life
of the individual.

Chemical investigation, however, to a certain
extent teaches considerably more than Morpho-
logy does. We shall prove this in our discussion of
chemical reactions in living matter.

Chemical changes in living substance con-
tinue without interruption as long as active
life prevails. So the chemist has to face great
difficulties when examining 4iving matter. From
his occupation with inorganic matter he will be
accustomed to see that no change takes place in
10

PROTOPLASM

the matter under investigation unless an experi-
ment be made.

We stand before the question as to what may be
made responsible for this continuous change of
form 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 of
importance. Only to the microscopical investiga-
tion of the cells do we owe our knowledge of the
organs of life. And here again animal cells have
proved to be much less accessible for searching
analysis than the cells of plants. It was in 1840
that Hugo von Mohl, of Tubingen, drew attention
to the important fact that plant cells have the
qualifications of life only as long as they contain
a slimy layer along the cell wall, which layer was
at first called the Primordial Utricle. The thorough
examination of anatomical facts led Mohl and
Schleiden to the conviction that all the organs
of the cell originate in this slimy matter. Con-
sequently the mucous layer was called Protoplasm.

In the following decades it was fully established
that the presence of life is extremely closely
connected with the presence of active protoplasm.
The physiologists Bruecke and Kuehne may be
called the originators of the view now universally
adopted that Protoplasm is the Living Substance
in animals and plants. The general and funda-
mental properties of protoplasm in both are the
ii

CHEMICAL PHENOMENA IN LIFE

same. But it was the merit of the well-known
botanist Ferdinand Cohn, of Breslau, that he
was the first to declare, in 1850, the identity of the
protoplasm in plant cells and of the so-called
Sarcode in animal cells.

The Chemistry of Life may henceforth be called
the Chemistry of Protoplasm. This is our territory
when we study Chemical Phenomena in Life.

The first work the chemist does when beginning
his examination of a substance, is to describe its
properties before they have been changed by any
reaction. We have also to specify the chemical
qualities of the substratum of life before we enter
upon the effects of reactions between protoplasm
and other substances brought into contact with it.

What is protoplasm chemically so called? Is
it to be considered as a substance peculiar to
living organisms and responsible for all the unique
phenomena by which life is characterised ?
Or is protoplasm a combination of different
substances peculiarly composed ? Or, finally, is
there any unknown structure in the mucous matter
which we call protoplasm, and should we not pre-
fer to speak, rather than of a substance or of a
combination of substances, of a minutely structured
organ when \ve deal with protoplasm ?

Morphology, however, and comparison with
other details of cell structure strongly uphold the
theory that protoplasm is an intricately con-
structed organ of the cell. It does not matter

12

PROTOPLASM

that even the powerful microscopes which the ad-
vanced technical perfection of our time has pro-
duced, cannot show any more minute morphological
details in protoplasm than some very small dark
granules or scarcely visible drops of liquid, spoken
of as Microsomes. But the exact and extremely
regular development in the evolution of the cell
organs, as well as the undoubted co-operation of
protoplasm and the nucleus in cell cleavage and
in fecundation, is the strongest affirmation of the
organ-theory of protoplasm. In consequence of
these facts, we prefer to speak of Cytoplasm in-
stead of protoplasm, when we characterise the
living substance of the cell, surrounding the
nucleus.

Experiment, too, seems to establish such a theory
very readily. When animal or plant tissue is
minutely pounded in a mortar, the pulpy mass
which we finally obtain is far from being an
organ, or from containing living cells. It is as
little a living thing as a watch remains
a watch after having been ground down to
powder. Notwithstanding this, the component
substances must have remained in either case.
It is clear that protoplasm is as little identical
with 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 must
lead us to the conclusion that protoplasm is not a
13

CHEMICAL PHENOMENA IN LIFE

mere orderless homogeneous combination of dif-
ferent substances or a peculiar substance in
itself. On the contrary, it renders it very probable
that structural characteristics play a most im-
portant part in living protoplasm, perhaps form
the essential trait in the organ of cell-life. Ex-
perimental Biochemistry of our days, however, has
been able to show that the characteristics of living
protoplasm are not all destroyed at once, when a
living organ is ground to a pulp. If care is taken
to ward off the effects of microbes which rapidly
develop in the remains of the tissues, by adding
some toluol or chloroform, a series of reactions
which are quite peculiar to life can be still observed
in the disorganised pulpy masses. This method of
preserving organs which have been minutely
ground down is much employed in modern
physiology. We call it Autolysis. It is possible
to prove that autolytic mixtures show the same
chemical processes as we find in the digestion of
food, in respiration and even in excretion. There-
fore we cannot concede that protoplasm is at
once destroyed when it is ground down as minutely
as possible. The death of protoplasm is no sudden
process. The reactions of life cease slowly and
successively one after the other.

Theories which maintain that protoplasm is

merely effective in life thfough its structure are

generally classified as the Engine-Theories of Life.

We see that such theories are right essentially,

14

PROTOPLASM

but that they do not exhaust their subject.
They leave unexplained all the phenomena of
life which continue in autolytic mixtures. All
the theories which lay stress upon the peculiar
chemical nature of protoplasm can be called the
Stuff -Theories of Life. Such a theory was that
which was kept in mind when Biology first began
the investigation of protoplasm. In consequence
of this view analyses were desirable. The analysis
of protoplasm should be as correct and complete
as possible, in order to show of what kind of
substance the substratum of life consists. The
difficulty was to collect a sufficient quantity of
pure protoplasm for analytical purposes. Reinke
and Rodewald in 1880 tried to solve this important
question by an extensive analysis of the mucous
plasmodium of Fuligo varians. This organism
consists of a yellow slimy matter, exactly com-
parable to the cell-protoplasm of other plants.
The result of this famous analysis was to show
that protoplasm consists of different organic
and inorganic compounds. The greater number
of the organic protoplasmatic substances, however,
were found to belong to protein matter, sensu lato.
About J or f of the dry substance of protoplasm
can be considered to be protein bodies. Of the
remainder about half were found to be fatty
bodies, sugar, and carbohydrates. The other
part contained different organic acids, of which
amino-acids may particularly be mentioned,

CHEMICAL PHENOMENA IN LIFE

different organic bases, finally mineral salts of
potassium, magnesium, and calcium.

Reinke and Rodewald drew from their different
experimental work the conclusion that protoplasm
could not be considered to be a specific organic
substance. It was rather a complex of various
organic and inorganic substances, none of which
was new to chemistry. In consequence of these
experiments the two German biologists inclined
to the opinion that it was not chemical and sub-
stantial properties which essentially characterised
protoplasm, but mainly the structure of the
protoplasmatic masses in living cells.

The impression made by this experimental work
upon biologists, both botanists and zoologists,
was so great that for a long series of years the
Engine- or Structure-Theory of protoplasm was
exclusively the prevailing one. The opinion of
Oscar Loew and some other eminent physiologists
that protoplasm must nevertheless contain some
peculiar matter which is characteristic of life Avas
scarcely taken up by any textbook authors or
University teachers.

The last decade, however, seems to have pre-
pared an alteration in the course of the biology
of protoplasm. As I have already mentioned,
chemical methods clearly show that in the pulp
prepared by grinding down living organs in a
mortar some vital phenomena continue for a
longer time. Therefore not all the Chemical
16

PROTOPLASM

Life is destroyed, even if cell-structure is as com-
pletely as possible annihilated. Consequently some
substances must exist in protoplasm which are
directly responsible for the life-processes, which
do not cease with the destruction of the cell.
And these substances are characteristic of living
protoplasm. For when the cell-pulp is heated to
the temperature of boiling water these chemical
processes cannot be any longer observed. The
remainder of the cells may then be considered as
definitely dead.

So we must come to the conclusion that, in
spite of the ingenious experiments and arguments
of Reinke and Rodewald, the comparison between
protoplasm and mechanical structure is not quite
an exact one. No mechanism is known which
would not be destroyed by minutely pounding it,
but which is destroyed by boiling water. And,
on the other hand, chemical alterations are quite
usually caused by a raised temperature, but
scarcely in any case by simply grinding down
the material. When we see that the substances
in living protoplasm are so easily destroyed by
heat, we are not surprised that the analysis of
protoplasm by Reinke and Rodewald could not
detect such constituent parts of living matter. At
present, however, it would be possible to carry
out exact analytical studies on protoplasm with
highly developed methods and with much more
success. Nevertheless, the literature of the last
c 17

CHEMICAL PHENOMENA IN LIFE

years does not contain more than a few reports
about analytical work on protoplasm. The great
difficulty in such investigations is to procure a
sufficient quantity of suitable material.

Nevertheless, we possess valuable papers on
the chemistry of protoplasm from special research
work done on animal and plant material. There
are results which clearly show the difficulties
met with in preparing the protoplasm-proteins
without any chemical change during the process of
separating them. There is no doubt that proto-
plasm contains highly complex proteins which
are very easily split up into more primitive protein
substances, even by treating them with very
dilute alkaline or acid solution, or even by keeping
them in a watery solution for a couple of hours
at ordinary laboratory temperature. Reinke's
opinion was that one of the protein bodies of his
preparation, the so-called Plastine, was the chief
constituent of protoplasm. Later, Etard was
fortunate enough to isolate complex protoplasm-
proteids of highly variable character. The
French chemist proposed to name these com-
pounds Protoplasmids. By more advanced methods
of quickly drying the cell protoplasm without
applying too high a temperature, zoochemists
succeeded in preparing a series of such Organ-
Proteids. We cannot but hope that the bio-
chemistry of protoplasm will in this way make con-
siderable progress. The successful investigations
18

PROTOPLASM

on the Enzymes marked a very important step
towards the discovery of the true chemical nature
of protoplasm. A special chapter has to be
dedicated to these remarkable substances, the
properties of which are eminently characteristic
of living matter.

The final result of our discussion is that there
are many reasons for maintaining that protoplasm
really is of a peculiar chemical constitution, and
that it does not merely represent a mechanical
structure. But we have to concede that the
chemical nature of protoplasm is not founded
upon the peculiarities of one particular substance
which is characteristic of living protoplasm. There
are, we are certain of it, a great number of con-
stituents of protoplasm which form the substratum
of cell-life.

CHAPTER III
PROTOPLASM AND COLLOID-CHEMISTRY

WE have been told in the foregoing chapter
that protoplasm is a slimy mass contain-
ing numerous organic compounds which chiefly
belong to the groups of proteins, carbohydrates,
and fatty bodies. The substances named here
represent for the chemist chemical bodies of
certain physical properties which, since the
famous investigations of Thomas Graham on
Liquid Diffusion applied to Analysis, in 1861, are
well known as colloidal properties. Colloids, the
prototype of which is glue, TO KoAAa, were charac-
terised by Graham as substances which scarcely
or not at all show diffusion through animal mem-
branes, and which cannot possibly be brought into
the shape of crystals. Colloids, therefore, form a
striking contrast to the common mineral salts
which readily show diffusion or Osmosis through
membranes, and which regularly appear as crystals
when the solution is concentrated and evaporated.
Graham spoke of this stage as the Crystalloid
Stage. For him, to use his own words, Colloids
and Crystalloids were two worlds of matter,
quite distinct and without any transition from one
to the other.

20

COLLOIDS IN PROTOPLASM

It marked an important progress in Biology
when the views of Thomas Graham were applied to
protoplasm. The manifestly colloidal nature of
living protoplasm demonstrated ad oculos the
significance of studies on colloids for Biology.
Protoplasm shows itself as an almost liquid slime
of the consistence of a liquid starch-paste or of a
strong solution of albumin, and never becomes solid.
Graham divided colloids, according to their more
liquid or more jelly-like consistence, into Sols and
Gels. There is no doubt that protoplasm has the
nature of a sol. While the knowledge of salt
solutions was being perfected in the 'seventies and
'eighties of the last century, colloidal solutions or
sols were also extensively studied. So it was
learned that colloidal sols differ from salt or true
solutions in a number of important points. Salt
solutions are always electrolytes, colloidal solutions
never are. Salt solutions have a lower freezing-
point and a higher boiling-point compared with the
medium of solution (water). Colloidal solutions
do not show any divergence from the two principal
points of temperature of the medium of solution.
Modern physical chemistry explains the proper-
ties of true solutions by the hypothesis that,
depending upon dilution and temperature, a larger
or smaller number of the dissolved molecules are
split up into smaller particles which are iden-
tical with Faraday's Ions. Colloidal solutions
do not conduct electric currents and do not show

21

CHEMICAL PHENOMENA IN LIFE

any difference in the osmotic pressure theoretically
calculated from the number of molecules. So we
must believe that colloidal solutions are never
electrolytes, but are always molecular solutions.

The depression of the freezing-point in solutions
is less in proportion as the molecular weight of
the substance dissolved is greater. If colloidal
solutions only show a very slight depression, or one
which lies beyond the limits of exact observation,
the conclusion is evident that colloidal substances
have a very considerable molecular weight. It
was extremely interesting for physiology to learn
that exactly those substances which are most im-
portant for life possess a very high molecular weight
and consequently very large molecules in com-
parison with inorganic matter. For example,
egg-albumin is said to have the molecular weight
of at least 15,000, starch more than 30,000, whilst
the molecular weight of hydrogen is 2, of sulphuric
acid and of potassium nitrate about 100, and the
molecular weight of the heaviest metal salts does
not exceed about 300.

Thus we come to the hypothesis that the size
of the molecules of dissolved colloids is considerably
larger than the size of those of crystalloids. It is of
great interest that in living protoplasm such large
molecules are characteristic of its chemical structure.

Graham believed that colloids and crystalloids
are not connected with each other by substances
of intermediate character. They were rather said

22

COLLOIDS IN PROTOPLASM

to differ very clearly. But now we know that
Natura non facit sallus, not even in colloid and
crystalloid matter. The chemistry of proteins
showed that typical colloids, for instance, egg-
albumin, are step by step transferred into typically
soluble substances when these proteins are split
up into the products of digestion by the working of
digestive ferments. The first products of de-
composition, the proteoses, show the typical
colloid properties, only slightly less marked than
the original protein. The peptones, the next
product of decomposition, are not crystallisable,
but are distinctly different from typical colloids.
Their molecular weight is certainly less than 1000,
and they are distinctly electrolytes. Another
example of an intermediate state between colloids
and crystalloids is demonstrated in soap solutions.
Both peptones and soaps are important and widely
spread constituents of cell-plasma. Such sub-
stances forming transitions from colloids to
crystalloids may be called Semicolloids. On the
other hand, we have to confess that we cannot
draw a sharp line of distinction between liquids
containing solid particles suspended and colloidal
solutions in which only molecules of a large size
can be present. These facts are of the greatest
importance for Biology.

The chemists Linder and Picton were able to
show how suspensions of the yellow sulphide of
arsenic are obtainable in particles of all sizes.
23

CHEMICAL PHENOMENA IN LIFE

From particles which were too heavy to remain
suspended and which sank quickly to the bottom,
a continual graduation was observed down kto
particles which were so small that they passed
through paper niters and were not even micro-
scopically visible. Bredig's experiments on plati-
num dispersed by the electric arc in water clearly
demonstrated that metallic platinum may be
obtained there in every imaginable size of particles.
The coarsest particles form a brown precipitate.
The finest of them stain the water dark brown
without any trace of turbidity, are not retained
by any filter, and no particle is microscopically
visible. The liquid has all the properties of a
colloidal solution of platinum.

The metal-sols, of which a large number have
already been obtained, are of great interest, since
we possess a new experimental help for studies of
colloids in the so-called Ultramicroscope. Tyndall
drew attention to the remarkable phenomenon that
rays of light remain visible in a liquid only when
particles suspended therein reflect the light. When
water is carefully freed from any trace of particles
of dust, we cannot follow the course of rays of light
through the liquid. The water rather appears to us
as itself diffusely lighted without showing the
stripes of light which are produced by a ray of
sunlight or electric light thrown upon a vessel
containing water. Colloidal solutions always
show TyndalTs Phenomenon. This experiment,
24

COLLOIDS IN PROTOPLASM

therefore, is very suitable to demonstrate the
existence of solid particles in colloidal solutions.

About ten years ago Zsigmondy, in Jena, very
ingeniously used the principle of Tyndall's pheno-
menon to show the single particles themselves
in colloid solutions by means of the microscope.
Whilst microscopical objects are usually illumi-
nated by rays of light so directed that they are
parallel to the axis of the microscope, Zsigmondy's
microscope was arranged in such a manner that a
very thin and strong ray of electric light was
thrown through the microscopical preparation
from the side, vertical to the axis of the micro-
scope. Consequently the microscopical field of
vision remained dark. The suspended particles,
when illuminated from the side, reflect the light
and become visible, appearing like small stars
on the dark sky. The strong dispersion of light
does not permit us to recognise the size and shape
of the single particles. But they can be counted
exactly. In this way the particles of platinum or
of gold-sols were made visible, and even their size
could be indirectly determined. An arrangement
was even made for studying living cells and
protoplasm by means of the ultramicroscope.
It was clearly shown that numerous particles in
protoplasm are made visible by this method which
could not be seen by the ordinary microscope. *

Ordinary microscopical observation with the
strongest lenses can show particles of about 250 /x/x
25

CHEMICAL PHENOMENA IN LIFE

in diameter. We call particles of and above this
size Microns. The ultramicroscope makes par-
ticles visible even down to the size of 6 /*/*, provided
that the power of light applied is strong enough.
Such particles are called Submicrons. But in
solutions of albumin or of starch-paste even the
ultramicroscope does not dissolve the cone of
light into single particles. Nevertheless, it is
highly probable that even in such solutions
separate particles exist which are smaller than
6 /M/A. Such are called Amicrons. The presence of
amicrons can be shown indirectly, for such
corpuscules readily become the nuclei of pre-
cipitates. When amicrons are present, precipita-
tion is more easily effected than without them.
The size of 6 //,/x in diameter is probably the size
of the albumin molecules themselves. Thus by
means of the ultramicroscope it has been made
possible to distinguish the largest molecules of
colloidal substances and to demonstrate the
reality of existence for the molecules. Submicrons,
however, are generally already aggregations of
molecules. In such a way we can get at least a
glimpse of the molecular structure of colloids,
and of protoplasm in particular. Protoplasm,
in the same way as colloidal solutions, must
generally be considered as a heterogeneous system.
Solid particles of different colloidal substances are
suspended in a liquid. The particles are of
different sizes. Some do not differ in size from
26

COLLOIDS IN PROTOPLASM

large molecules, some form aggregations of mole-
cules, others consist of small masses of the sus-
pended substance, others finally are but coarse
particles, already subjected to the force of gravi-
tation, and, if allowed, quietly deposit. The
particles, besides, may be of different physical
conditions, either liquid drops or solid bodies.

Colloidal solutions, indeed, show quite a different
physical behaviour if the suspended particles
vary in size and in physical condition. In the
first case it is advisable to divide the colloidal
solutions into several groups according to the
solid or liquid state of the suspended particles.
Colloidal solutions which contain solid particles
may be called Suspensions, such as contain small
suspended drops of liquids may be named Emul-
sions. Instead of drops there may even occur in
colloids small bubbles of gas. Then the colloid
system more or less resembles froth. It is possible
that even in protoplasm small bubbles of gas are
included, forming a very fine foam.

According to the size of the suspended particles,
all these colloids show well-marked physical
differences. When the particles are comparatively
large the constitution of the system is as a rule
very unstable, and the particles are inclined to
deposit. Such suspensions are scarcely to be con-
sidered as colloidal systems, but rather as a transi-
tion stage to colloids. Protoplasm must to a
certain extent have the properties of such a sus-
27

CHEMICAL PHENOMENA IN LIFE

pension. We must therefore ask what character-
istics are found in these suspensions. Such
systems have in general the properties of the
liquid medium. The specific weight, viscosity,
and surface tension do not differ from the value
found for the medium, and so it is with regard
to the freezing-point, the boiling-point, and the
power of conducting electric currents. We may
understand this to be due to the comparatively
small quantity of the suspended substance in
proportion to the quantity of the liquid medium.
Such suspension systems do not in any way re-
semble solutions. Here we may mention the so-
called phenomenon of Cataphorcsis in these
suspensions. When an electric current passes
through the suspension, the particles migrate to
the anode or to the cathode, corresponding to the
specific character of the suspension. This pheno-
menon, which has been thoroughly discussed by
physical chemists, has not yet shown itself to be
of any great importance for the chemistry of
protoplasm.

Whilst suspensions with comparatively large
particles can be recognised as suspensions by
ordinary microscopical observation, the particles
in other colloidal solutions can be discovered only
by means of the ultramicroscope. We have
mentioned that protoplasm contains ultramicro-
scopic particles or submicrons, which are not seen
but by ultramicroscopic investigation. All these
28

COLLOIDS IN PROTOPLASM

colloids may be called Suspension Colloids. From
coarse suspensions to suspension colloids there
exist all kinds of intermediate suspensions. The
platinum sol and the other metal sols mentioned
above belong, according to their action and to their
physical properties, to the suspension colloids.
They have been of great use in studies on suspen-
sion colloids. Quantitative analysis showed that
even in suspension colloids the amount of the
solid phase is very small in comparison with the
quantity of the liquid medium Suspension colloids
have very few points of resemblance with solutions.
They do not conduct electric currents but to a
slight extent, and they do not show alteration
from the freezing-point of their liquid medium.
Cataphoresis has been quite generally noticed
even in suspension colloids. In fact, suspension
colloids are nothing else but cases of ultramicro-
scopic suspension. The only one important differ-
ence from coarse suspensions is the great stability
of suspension colloids. Platinum sol or the colloid
solution of hydroxide of iron or any other suspen-
sion colloid may be kept for years without showing
any alteration. Since the suspended particles are
considerably smaller, we must believe that the
surface of contact between the suspended substance
and the medium (we speak nowadays of the
Medium of Dispersion] is much larger in suspension
colloids than in coarse suspensions. We may con-
sider this to be the reason for the greater stability
29

CHEMICAL PHENOMENA IN LIFE

of the former. Of great chemical and biological
interest is the effect of small amounts of salts, i.e.
electrolytes, on suspension colloids. If we prepare
a colloidal suspension of mastic resin in water by
mixing one drop of alcoholic mastic solution
with a large quantity of water, and add to the
milky liquid a trace of mineral salt solution, after
a couple of seconds white flakes of deposit appear
in the colourless liquid, and the whole resin
colloid is precipitated in flakes. We do not doubt,
and our opinion is confirmed by the noteworthy
experimental work of Hardy, Bredig, and others,
that the electric properties of the colloid play the
chief part in this flaking-phenomenon. We have to
think that the colloid particles are aggregated or
agglutinised by electric influence, and form a
deposit when they have reached a certain stage of
aggregation. Probably the particles charged with
positive or negative electricity attract ions of the
contrary charge. Since ions have a much stronger
electric charge than colloid particles, one ion may
attract a number of colloid particles. By this process
there must be formed large masses of the colloid,
which are no longer able to remain suspended in
the liquid, and form flakes which slowly deposit.

All colloid solutions or sols which do not show
any separate particles either by means of the
ordinary microscope or by the ultramicroscope,
are at present united under the name of Emulsion
Colloids. There is no doubt that just such colloids

30

COLLOIDS IN PROTOPLASM

are the most important constituents of protoplasm.
The physical properties of Emulsion Colloids are
very characteristic in comparison with those
of the suspension colloids. The optical and
electrical methods which are so useful in study-
ing suspension colloids do not show remarkable
results in emulsion colloids. The suspended
particles are so small that their existence can only
indirectly be proved by the Tyndall phenomenon.
The particles in suspension colloids are charged
with a certain kind of electricity. The organic
colloids and the metals of the group of platinum
are charged with negative electricity, the hydroxide
sols of iron, aluminium, etc., with positive electri-
city. The kind of electricity never changes. In
consequence of this positive Colloids may be
precipitated by negatively electric colloids and
vice versa, but colloids of the same electric charge
are never precipitated by each other. The electric
conditions are quite different in emulsion colloids.
Cataphoresis can be shown, but working more
slowly. On the contrary, a very remarkable
characteristic of emulsion colloids is that the kind
of electricity with which they are charged can be
easily changed. Thus albumin particles can be
charged either with positive or with negative
electricity. It depends upon the chemical con-
dition of the medium of solution which electricity
is accepted by the albumin particles. If the
reaction of the medium is alkaline, the particles are

31

CHEMICAL PHENOMENA IN LIFE

negatively electric, but in acid medium they are
charged with positive electricity. Emulsion
colloids also show quite a different reaction to
small quantities of electrolytes. Emulsion colloids
are never precipitated by a small amount of
mineral salts. The electric properties of the ions
cannot alter the colloid state.

Otherwise emulsion colloids in many respects
resemble real solutions. In the first place, the
diffusion of emulsion colloids is considerable
enough to be measured by means of the usual con-
trivances for studying diffusion phenomena. Such
experiments had already been made by Graham.
Later on, Pfeffer carried out experiments on
solutions of gum-arabic and glue, to show that
distinct osmotic pressure can be observed to be
exercised by such colloids. The osmotic pressure,
however, is very small as compared with the osmotic
effects of sugar solution or of inorganic salts.
Even the freezing-point of emulsion colloids is dis-
tinctly lower than the freezing-point of the pure
medium. Such sols show many transition charac-
teristics to true solutions. The density of sols is
distinctly different from the specific gravity of the
pure medium. The surface tension of sols also
differs regularly from the surface tension of the
pure medium. In many cases the surface tension
of water is lowered by dissolving colloids in it.

Such characteristics are to be expected in the
emulsion colloids of protoplasm. Protoplasm,
32

COLLOIDS IN PROTOPLASM

therefore, has many of the physical and chemical
characteristics of true solutions. On the other
hand, properties must be present in protoplasm
which are only found in suspensions. We see
that such a state of things is very favourable
for the action and counteraction of many sub-
stances in the narrow territory of the protoplasm
of one cell. Water is without doubt the medium of
solution in protoplasm. Many substances, chiefly
of the groups of protein bodies and carbohydrates,
form the mucous emulsion colloid which is the
fundamental mass of protoplasm. Protoplasm is
practically an albumin sol. We remember that
fatty substances are regular constituents of proto-
plasm. They are not soluble in watery mediums,
but they may be brought into the form of colloid
solution in water, either only into the stage of
suspension colloids, as we can see on shaking oil
and water together, or even into the stage of
emulsion colloids. The latter can be reached by
adding a trace of potassium carbonate to the
mixture of oil and water. It is sufficient to shake
the mixture for a very short time to form a milky
liquid of great stability, which can be filtered
without change. The physical properties of such
oil emulsions are the properties of emulsion colloids.
In protoplasm fats must be present in the form of
suspension colloids and of emulsion colloids. Other
substances insoluble in water must be present in
similar^forms.

D 33

CHEMICAL PHENOMENA IN LIFE

It may be that the whole mass of protoplasm
is not equally rich in these suspensions. As a rule
we perceive along the cell wall on the outmost
layer of protoplasm a thin protoplasmatic part
which does not show any visible particles, and
only very few under the ultramicroscope. This
layer was named by Pfeffer Hyaloplasma. The
other parts of protoplasm usually contain great
quantities of coarser particles which give a greyish
colour to the whole protoplasmatic mass. Pfeffer
introduced the name of Polioplasma for this part
of the cytoplasma.

It is manifest that Hyaloplasm is an important
medium to admit substances from outside into
the cell as well as to permit the passing out of
products of the cell. Hyaloplasm can therefore be
considered to be the cell organ for the Endosmosis
and Exosmosis of substances, i.e. the osmotic
organ of cell protoplasm. Polioplasm, on the
other hand, must be the organ to assimilate the
substances which enter the cell, to form new
constituents of protoplasm, to furnish different
forms of physical energy, to continue the process
of life and to form the substances which are
superfluous for cellplasm and are excretions.
Polioplasm is thus the seat of the metabolism
of the cell itself. We shall try to show how far our
present chemical knowledge may explain the
connection of all these functions of living cell
protoplasm.

CHAPTER IV

THE OUTER PROTOPLASMATIC MEMBRANE
AND ITS CHEMICAL FUNCTIONS

BESIDES the transparent condition and the
absence of coarser granules or microsomes
hyaloplasm exhibits a series of microscopical
peculiarities. It is well known that protoplasm
in living plant cells generally shows a streaming
movement which is easily recognised either by the
movement of the chlorophyll bodies themselves
or by that of the microsomes. These bodies are
carried along by the streaming protoplasm with
considerable velocity. Even the cell nucleus is in
some cases carried along by the current of stream-
ing protoplasm. This outer transparent layer is
continually at rest, is never made turbid by
particles, and never includes drops. of liquid, cell
sap, which is quite commonly found in the polio-
plasm of older cells. Perhaps the viscosity of
hyaloplasm is greater than that of polioplasm. In
any case the boundary lamella of the hyaloplasm
must be of tougher consistence, and may be well
considered to be a plasmatic membrane or boundary
membrane of the living parts of the cell. This
plasmatic membrane is the proper organ for
35

CHEMICAL PHENOMENA IN LIFE

regulating the osmotic change of substances
with the outer world. While the cellulose mem-
brane of the cell is only a dead cover of the living
contents, the living plasmatic membrane is
variable in its condition and is quite different
when in its normal living state and when dead.
If slices of beet-root are dipped in water, after
having the remainder of the cells which were cut
through properly washed off, one may keep them
in water for any length of time without losing
even a trace of the red colouring matter in the
living cells. But if chloroform is added to the
water and the cells are killed by the narcotic
agent, streams of red colour go out from the
tissue. 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 cell
lies with the protoplasmatic membrane. Even
the well-known fact that the chemical constitution
of plants is quite different from that of the soil in
- which they are growing, proves the elective in-
fluence of the protoplasmatic membrane in
endosmosis. This elective influence is much
better shown by the phenomenon of Plasmolysis.

We owe to Hugo de Vries, of Amsterdam, the
excellent method here described. It is best to
choose cells with red-coloured cell sap for the
experiments. Such cells are found on the under
surface of many leaves. Corollary petals may also

36

THE PROTOPLASMATIC MEMBRANE

well serve the purpose, but they are not so easily
cut with the razor. When such sections are put
into salt solution of sufficient concentration, e.g.
potassium nitrate 2 per cent, after some minutes
all cells show their protoplasm shrunk away
from the cell wall. The cell protoplasm forms a
red ball lying free in the cell. When the sections
are put back into water, the plasmolysis disappears
and the cells regain their normal condition.
Plasmolysis is therefore a normal, merely physical
phenomenon, not at all a pathological one.

How can plasmolysis be explained ? Micro-
scopical inspection immediately convinces us of
the fact that the volume of protoplasm is reduced
in plasmolysis. It was only possible for this to be
brought about by the expulsion of water fronr'the
sap vacuole of the protoplast. By loss of water the
concentration of the sap is increased, until the
osmotic value of the outer solution is greater than
the osmotic value of the cell sap. This state being
arrived at, equilibrium is regained. We learn
from this process that the protoplasmatic mem-
brane cannot be permeable for the salt in solution.
If it had been permeable, the equilibrium would
have been reached simply by endosmosis into the
cell, as long as the concentration inside and outside
had not become equivalent. Or osmotic substances
would have penetrated the protoplasmatic mem-
brane from the inside of the cell when plasmolysis
disappeared in water. Consequently, wo may say
37

CHEMICAL PHENOMENA IN LIFE

that the plasmolytic power of a certain solution
proves distinctly that the substance cannot pass
through the living protoplasmatic membrane.
If the solution does not effect any plasmolysis,
we may be sure that the substance enters the cell
more or less considerably.

Ernest Overton was the first who thoroughly
investigated these interesting problems in 1895.
He found that mon-acid alcohols, aldehydes,
and ketones, also esters of fatty acids and
alkaloids, produce least plasmolysis. As a rule
it is impossible to bring about plasmolysis by
means of these substances. They enter the cell
very easily and pass through the plasmatic
membrane without any difficulty. Glycols and
amino-compounds cause plasmolysis a little more
readily. With glycerin or erythrite it is still
easier to bring about plasmolysis. But the sugars
and the substances most closely related (for
instance, mannite), the amino-acids and the salts
of organic acids very readily produce plasmolysis.
They cannot pass through the protoplasmatic
membrane but with great difficulty. Finally, the
salts of inorganic substances very quickly cause
plasmolysis, since they very slowly pass the
plasmatic membrane, or practically do not pass
the boundary of protoplasm. Overton added to his
valuable experiments a most ingenious conclusion.
He drew attention to the fact that just such
substances easily pass through the protoplasmatic

38

THE PROTOPLASMATIC MEMBRANE

membrane as are soluble in fat. This is the reason
why chloroform and ether are so readily taken up
by the cell. Overton showed further that the
phenomenon of narcosis is principally founded
upon the storing of chloroform by the fatty com-
pounds which are most important constituents
in the nervous system. Overton's theory was at
last confirmed by experiments on aniline dyes.
These substances as a rule are soluble only in
alcohol or in such organic liquids as dissolve fatty
compounds. They are readily taken up by cells.
It is easy to prepare from such colouring matters
compounds which are soluble in water. This is
done by treating them with sulphuric acid. The
sulphonic acids thus obtained are substances
soluble in water, but insoluble in ether or alcohol.
Such solutions cannot enter living cells.

The conclusion finally drawn by Overton from
all these facts was this, that protoplasm is en-
veloped in a thin layer which is either rich in fatty
substances or is a thin film of fat or oil, as was the
opinion expressed by the German physicist
Quincke some years before Overton's work
appeared.

There are many facts, indeed, which seem to
make such a theory very plausible. Living
protoplasm always acts as liquids do in a state of
equilibrium. When it enters a state of rest it
assumes the shape of a sphere. Such action can
be quite distinctly seen in amceba when they are
39

CHEMICAL PHENOMENA IN LIFE

preparing for the resting state. Plasmolysed
protoplasm has the same inclination. We see
that protoplasm in rest has the tendency to
diminish its surface as far as possible in
proportion to its mass or its volume. The
spherical surface is the geometrical minimum of
surface for a certain volume. From this pheno-
menon we learn that the force of surface tension
must in some way regulate the outlines of living
protoplasm. When the living protoplasm of an
amoeba stretches out its so-called Pseudopodia
on one side, and draws in the projecting parts on
the other, thus creeping slowly over the moist
ground, variations in the surface tension on
different parts of the circumference of the cell
must take place. The surface tension must increase
when new prominences are formed, and surface
tension must diminish whenever Pseudopodia
are drawn in. But such alterations in surface
tension presume certain chemical changes in the
boundary layer of the cell, and formation of
substances which show different surface tension in
comparison with the foregoing state. We learn,
further, that such chemical processes must be
reversible, to be repeated whenever needed in cell
life. In water protoplasm always shows a dis-
tinctly lower surface tension to the watery medium
than mucous protein substances or carbohydrates.
It always rounds to spherical shape when in
rest.

40

THE PROTOPLASMATIC MEMBRANE

We owe to the famous thermodynamic studies
by Willard Gibbs, the eminent American scientist,
the theoretical basis for the knowledge of the
behaviour of different substances in compound
systems which possess different surface activity.
If these substances have the power of diminishing
the surface tension of the medium, they always
show the tendency to accumulate on the surface.
If there are several such substances, then that
substance which most depresses the surface
tension, or is most surface-active, is generally
accumulated in the surface layer. Upon the
basis of Willard Gibbs' theory we may expect in
advance that all the protoplasmatic substances
which have the strongest power of depressing
surface tension, such as fats, must necessarily be
collected upon the surface of protoplasm. So
Overton's hypothesis is confirmed by several
arguments, and we may consider it to mark an
important progress in the chemistry of protoplasm.
In the course of these investigations it was highly
desirable that we should be enabled to measure
the surface tension of living protoplasm, and to
compare the surface tension of protoplasm with
the figures obtained for the surface tension of
different substances. The difficulties, however,
were great and could not be overcome till lately.
The advance sought for came from studies on the
toxic effects of alcohols on living cells. Traube, in
Berlin, showed that the well-known law of the
41

CHEMICAL PHENOMENA IN LIFE

poisonous effects of alcohols, generally called
Richardson's Law, that the higher members of the
series of alcohols are more poisonous than the lower
ones, was connected with the capillary properties
or the surface tension of the alcohols. The German
chemist proved that the surface activity of the
alcohols increases from one member to the following
one in the same series in the ratio 1:3. A glance
at the results obtained by Overton and others on
the poisonous effects of alcohols immediately
showed Traube that the toxic effect increases in the
same proportion. The law of surface activity
and 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 organic
solutions on plant cells I noticed that the exos-
mosis of substances from the cell vacuole, con-
sequently the death of cells, regularly took place
when the surface tension of the solution had reached
the same degree. Most plant cells are injured and
die when a solution is applied which has the
surface tension of about two-thirds relatively to
that of water. No alcohol, no ether nor narcotic
has been found which did not affect the cell in a
solution of such a surface activity. But all sub-
stances of the most different chemical character
began to injure the cell just when the surface
tension had reached the critical point. Since all
42

THE PROTOPLASMATIC MEMBRANE

alcohols, ethers, ketones, and many other sub-
stances obey the same physiological law, we must
conclude that all these substances have the same
physiological effect upon living protoplasm. If
we consider that according to Willard Gibbs'
theory a substance of higher surface activity,
when brought into contact with protoplasm, must
necessarily displace the active substances of the
superficial layer, we see that disorganisation of
the structure of this layer must be the conse-
quence. We understand that exosmosis must
take place. This effect is always exercised when-
ever the concentration of the substance exceeds
the critical degree of surface tension. This degree
therefore must be slightly below the real value of
protoplasmatic surface tension. Consequently we
measure also the surface tension of protoplasm,
when we apply alcohol or any other solution of
the critical capillarity. Practically we may take
the surface tension of common plant cells as
equivalent to the surface tension of n % ethyl
alcohol.

This result forces us to raise the question why
the surface tension of protoplasm has just this
value and no other. Further experiments on the
working of fatty emulsions on living cells showed
me that poisonous effects such as are produced by
alcohols can be caused even by emulsions of fatty
bodies, that is, by colloid solutions. The only
condition is that the surface tension should be low

43

CHEMICAL PHENOMENA IN LIFE

enough to affect the superficial layer of proto-
plasm. So lecithin or cholesterin emulsions
are quite as effective as true surface-active solu-
tions. But emulsions of neutral fats never produce
toxic effects. The determination of the amount of
surface tension in emulsions of neutral fats as
highly concentrated as possible, gave the result
that such emulsions regularly depress the surface
tension to two-thirds of the value of that of pure
water. Since fatty compounds are always present
in protoplasm, it does not seem to be by chance
that the surface tension of living protoplasm
and the surface tension of fat emulsions are
practically the same. The conclusion may
perhaps therefore be drawn that the superficial
layer 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 an
oily film or a very thin layer of fat (Overton
thought of lecithin or cholesterin) does not seem
to be quite a correct one. The ordinary food of
plants consists of watery solutions of substances
which are usually not soluble in fat. It is, as I
think, more probable that the fat in the plasmatic
membrane is present in the form of an emulsion
of extreme fineness. The interstitial space
between the fat-globules must be filled up with a
watery colloid solution, most probably a protein

44

THE PROTOPLASMATIC MEMBRANE

sol. So the plasmatic membrane would in my
opinion consist of two phases. One, the lipoid
phase, 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 dis-
solved substances through membranes, has under-
gone many changes. There was a time when it
was generally believed that the diosmosis of a
substance depended upon the size of the pores of the
membrane and the size of the molecules of the
dissolved substance. Diosmosis cannot take place
when the pores are too small to let the molecules
pass. The membrane was considered to act like a
sieve for the molecules. This hypothesis does not
explain why fatty substances cannot pass mem-
branes which have taken up water. All signs show
rather that solution affinities play the most
important part in diosmosis. The membrane is
always permeable for a certain substance, when
this substance is soluble in the material of the
membrane. Nernst demonstrated this view by a
clear experiment. Ether is soluble in water as
well as in benzene. Benzene is soluble in ether only,
and insoluble in water. When a quantity of ben-
zene and a quantity of ether are separated from
each other by a layer of water, it is to be expected
that the ether will go through the layer of water,
but not the benzene. A continuous stream of
ether will pass through the water, but no stream
45

CHEMICAL PHENOMENA IN LIFE

of benzene in the contrary direction. An osmotic
pressure must be produced, therefore, in the
system on the side of the benzene. When the ex-
periment is carried out animal membrane saturated
with water is placed, instead of a layer of liquid
water, between the ether and the benzene. The
benzene is poured into a glass funnel connected
with a glass tube, and the funnel is closed with the
saturated membrane. Then the funnel is dipped
into a vessel containing ether. After a certain
time the liquid rising in the glass tube shows the
endosmotic streaming in of ether, subsequently the
osmotic pressure.

In the foregoing description the term Plasmatic
Membrane has often been employed for the super-
ficial layer of hyaloplasm. We have to justify the
choice of this expression. Membranes are films of
firmer consistence than the material, viz. the
liquid upon the surface of which they are formed.
So the expression plasmatic membrane implies a
firmer consistence for this layer than for the
hyaloplasm itself. We know from daily experience
that a colloidarsolution such as a solution of albu-
min or starch paste, is inclined to form a thin film
on the surface, which has almost the physical con-
dition of a solid substance. Protoplasm, being a
colloidal system, will most probably not differ from
other colloids in this respect. We notice, indeed,
after a lesion 'of a'cell when the cell and its proto-
plasm have been cut through, that the surface of the
46

THE PROTOPLASMATIC MEMBRANE

wound is quickly covered with a fine film. This
may be seen very distinctly in the wide cell tubes
of the marine alga Caulerpa prolifera. The film-
like excretion protects the protoplasm from any
further injury from water oozing in. Consequently
the whole hyaloplasm layer in the wounded spot is
soon regenerated.

The formation of membranes and of films is,
then, a general characteristic of protoplasm and of
colloids. This goes so far that it is possible to
deprive an albumin solution entirely of its contents
of albumin by shaking it. The albumin at once
becomes insoluble. We see thus how unstable
many colloids are. It has been already men-
tioned in a former chapter that a minimum of salt
solution is sufficient to precipitate suspension col-
loids. But to bring about the flaking out of emulsion
colloids by means of salts, we must add com-
paratively large quantities of mineral salts. There
is no doubt that the effect of salts on emulsion
colloids is in many respects allied to the effects of
dissolving. Between the particles of the colloid
and the salt there must be some solution-affinities
which do not exist in suspension colloids. In con-
sequence of this characteristic Perrin has proposed
to name the suspension colloids Lyophobic Colloids,
because there no solution affinities play any part,
and to name the emulsion colloids Lyophil Colloids
from their connection with real solutions. Durable
films are formed especially by precipitated
47

CHEMICAL PHENOMENA IN LIFE

suspension colloids. Such precipitations are not
reversible. When, on the other hand, albumin is
precipitated by sodium chloride, it is possible to
again dissolve the precipitation by diluting it
with water. This process is reversible. Generally
in albumin all precipitations with the salts of the
light alkaline metals and of magnesium are
reversible. But they are not reversible when
precipitated by copper salts, iron salts, or any other
salt of heavy metals. Precipitations with calcium
or strontium salts are inclined to be quite insoluble
in water. It is noteworthy that the working of the
salt depends upon the acid contained in it. Francis
Hofmeister, of Strassburg, was the first to show
that alkaline metal salts of different acids have a
certain graduated effect on colloid solutions.
They may be arranged in the following way,
beginning with the acid which precipitates most
quickly :

Citrate, Tartrate, Sulphate, Acetate, Chloride,
Nitrate, Chlorate.

This law became of the greatest importance in
the chemistry of colloids. It is not only applic-
able to the transition of colloid solutions into solid
colloids, 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 very

different. Glue itself, when quite dry, forms a

48

THE PROTOPLASMATIC MEMBRANE

horny mass, hard, inflexible, and brittle. When it
is more or less saturated with water, it becomes
flexible, viscous, then gelatinous, and in the
course of imbibition with water it approaches the
liquid state. Many gels have the character of a
gelatinous mass. Some, as gum-arabic, finally
dissolve entirely. Others, as cherry gum, swell in
water to a jelly and never dissolve. Doubtless
gels are of great importance in plasmatic structure.
They are formed in plasmatic colloids by many
influences, such as surface tension, electrolytes,
and the mutual precipitating effects of colloids.
Wherever protoplasm sols meet precipitating in-
fluences, films must be formed, which separate the
different parts from each other. Such gel-mem-
branes, on the other hand, play the part of semi-
permeable filters. Some substances are soluble in
them, and consequently pass through, but other
substances being insoluble in the gel substance are
retained. There is still another retention of
substances in gels which is not a consequence of
their insolubility, but, on the contrary, must be
traced back to some affinity of the substance
retained with the gel colloid. We call this process
of retention Adsorption of Substances. There is
no doubt that adsorption is of the greatest im-
portance for chemical processes in life. We have
especially to consider that the resorption of dis-
solved substances by cell protoplasm from the
surrounding liquids must be connected with ad-

*- 49

CHEMICAL PHENOMENA IN LIFE

sorption in protoplasm colloids. Taking up food
by hyaloplasm is consequently as inseparable
from adsorption in the colloidal matter of the
plasmatic membrane, as from solution in the fatty
substances of the superficial layer of protoplasm.

Essentially adsorption cannot be separated
from the swelling of gels in water. Many experi-
ments have shown that all influences which further
the swelling of gels hinder adsorption and vice
versa. Hofmeister's Law was found to be in force
even in this group of phenomena. The anions of
acids which are most effective in precipitating sols
are the same which are most adsorbed.

When adsorption of salts takes place by living
cells or by colloids, the electric state of the colloid
is very frequently of great influence on the process
of adsorption. Most of the organic colloids are,
as was shown above, negatively electric. They
must consequently act like acid anions, and
will in adsorption chiefly attract the bases of the
salts. If the salt is in a highly diluted state
practically adsorption only of ions can take place.
Mainly the cations, viz. the metal ions, are re-
tained by adsorption, while the anions remain to a
certain extent unaffected. Hence, of course, must
result reactions of acids, without any chemical
production of acids. Doubtless such adsorption
phenomena are of great interest for physiology.
It has for a long time been well known that roots
of plants produce the effect of acids upon the soil

5°

THE PROTOPLASMATIC MEMBRANE

and its constituents. It is possible to show this
by letting roots grow along polished marble plates.
After some weeks the marble surface clearly
demonstrates the dissolving effect of growing
roots and root-hairs. Delicate traces are every-
where etched in the marble surface, where roots
have come into close contact with the plate. I
was able to show, in 1894, that carbonic acid is
certainly to a great extent responsible for this
phenomenon. I made plates of plaster of Paris
mixed with different substances, the solubility of
which in water saturated with carbonic acid,
had been well considered. I discovered that
only such compounds are dissolved by the plant
roots and their excretion, as were distinctly soluble
in carbonic acid. These were phosphate of
calcium and strontium, but not aluminium
phosphate, which is dissoluble by carbonic acid.
Nevertheless, there are other effects of acids in
plant roots which cannot possibly be due to
carbonic acid, and which have not been ex-
plained until lately. Now it is believed to be
highly probable that merely the adsorption effect
takes part in these phenomena, and no excretion
of acids by the roots is to be assumed. If the
•cations are adsorbed and anions of acids remain
reactions of acids must result as well as in real ex-
cretion of acids. Now we can understand why
acids could not be discovered in the excretion
drops of the root-hairs, and why they react quite

CHEMICAL PHENOMENA IN LIFE

neutrally. Most probably even the acid properties
of peat and of Humic Acids of the soil can be
attributed to colloidal elective adsorption. The
negatively electric colloids of the peat moss
retain, as Baumann and Gully have lately shown,
chiefly the basic ions of the dissolved salts, and this
adsorptive election must lead to reactions of acid
in the soil extract. It can easily be demonstrated
that the citrate and the tartrate are most adsorbed
and productive more of the effect of an acid than
other salts of the same alkaline metal. I cannot
but suppose that the taking up of dissolved salts
by living cells is essentially founded upon pheno-
mena of adsorption. This opinion has been con-
firmed by the chemical analysis of peat moss by
Baumann and Gully. It was found that the
quantities of the basic mineral constituents of the
moss-ash are almost the same as are adsorbed
by the plant from the soil. Long ago agricultural
chemists had stated that the constitution of the
ash of plants which grow upon the same territory
may widely differ. This elective assimilation of
soil constituents may be now explained to a
great extent by the adsorptive qualities of the
colloids of the living cells.

In summing up we may say that the super-
ficial layer of cell protoplasm, called hyaloplasm,
may be considered to be a film of more solid con-
stitution which we call the plasmatic membrane.
This membrane regulates the change of substances
52

THE PROTOPLASMATIC MEMBRANE

in the metabolism of the cell, the assimilation of
food taken up from outside the cell and the
excretion of substances from the cell. The
plasmatic membrane is not completely permeable
for all substances, but has a so-called semi-
permeable layer, which permits some substances
to pass through and others not. The protoplas-
matic membrane is a compound colloid system
consisting of an extremely fine fat emulsion sus-
pended in a hydrosol, probably an albuminous
colloidal solution. We see, then, that fatty bodies
are taken up as well as watery solutions. Con-
cerning the latter, we are able to show how im-
portant adsorption phenomena are in assimilating
them. The laws of adsorption govern the assimi-
lation of salts from the soil. Even the action of
acids can be produced by adsorptive election.

So we may say that a great many phenomena
in life once attributed to Life Force, and not to be
explained by chemical laws, can in the present
stage of science be reduced to the general Laws of
Nature.

53

CHAPTER V

CHEMICAL PHENOMENA IN CYTOPLASM
AND NUCLEUS OF LIVING CELLS

r I ^HE main body of protoplasm, which is
JL surrounded by the hyalin layer of the
superficial cell plasma, generally contains finely-
granulated, slimy masses of a yellowish grey hue,
whence it is named Polioplasm. The appearance
of polioplasm is very different according to the age
and the stage of life of the cells. Quite young cells
are found equally filled with homogeneous polio-
plasm. In the midst of this protoplasmatic mass
one perceives a spherical body of more solid condi-
tion which refracts light strongly : the Nucleus of
the cell. In the course of growth the polioplasm
soon produces drops of liquid contents in greater
or smaller number. These drops increase in size,
and the polioplasm between them changes into
thin lamellae separating the contiguous cavities.
The polioplasma gains the character of foam.
The cavities between the meshes of tough colloid
mass are generally known as vacuoles. The further
development shows the conflux of several neigh-
bour vacuoles to one of larger size. The meshes of
54

CYTOPLASM AND NUCLEUS

protoplasmatic threads and lamellae become finer
and rarer. Only along the cell wall a thick
polioplasmatic layer persists. At last, when the cell
has nearly reached the definite size, we see, as a
rule, only the polioplasma layer along the cell wall,
surrounding one large vacuole which occupies the
whole central space of the cell. Even the nucleus,
formerly suspended on numerous fine plasmatic
threads and lamellae in the middle of the cell, is now
situated in the plasma layer near the wall, forming
a protuberance in this layer. The general im-
pression is that the mass of protoplasm does not
increase when cells are growing in length and
diameter. The nucleus even looks a little smaller
in adult cells than in young ones. Further, the
protoplasma must take up a considerable quantity
of water to form the vacuoles and to fill them with
a watery solution of different substances, which
solution is known as cell sap. Doubtless the
mechanism employed in forming vacuoles is con-
nected with the mechanism of growth. The whole
bulk of polioplasma does not swell when cells are
growing. The quantity of water in polioplasma it-
self seems to remain constant during the formation
of cell sap in the vacuoles.

It is noteworthy that the polioplasma remains
pressed against the cell wall. Loss of water im-
mediately disturbs this normal state. Leaves,
when withering, lose their normal elastic and firm
condition, and at once their capacity of growth.

55

CHEMICAL PHENOMENA IN LIFE

Distinctly the same effect is produced by the
action of salt solution. A flower stalk or leaf stalk
of fleshy consistence put into potassium nitrate
of about 2 per cent very soon becomes unelastic,
flexible, like a withered plant, and shortens its
length by some millimetres in a length of about
10 centimetres. We learn from this phenomenon
that the pressing of protoplasm against the cell-
wall is due to osmotic forces. Hugo De Vries
showed, in 1884, that it is possible to use the
suppression of osmotic pressure in cells or of the
Cell Turgor, as botanists say, by salt solution,
for the measurement of the osmotic pressure in
normal cells. The procedure is essentially identical
with the so-called plasmolysis we have spoken of
in a previous chapter. One has to apply solutions
of a pure mineral salt of different concentrations.
It is usual to take potassium nitrate because it is
easily available in quite pure preparations and
because the percentage in solutions is nearly
identical with the standard gauge in chemical
work, the Gramm Molecule Solution. Solution of
potassium nitrate containing 10-1 gr. in 100 gr.
water is only slightly more than 10 per cent con-
centration, and is a molecular solution, containing
one gramm molecule potassium nitrate, 101 gr. in
I litre of water. If we put sections of plant
tissue in different potassium nitrate solutions from
0-05 normal to 0-2 normal strength, we find that
the separating of the protoplasm from the walls

CYTOPLASM AND NUCLEUS

begins in solutions of about 0-12 to 0-15 normal
strength. This salt concentration gives us a
gauge for the amount of turgor. De Vries showed
that all salts produce the same result at the same
concentration in gramm molecules. We call such
solutions which have the same osmotic effect
Isosmotic Solutions. If we are able to directly
measure the osmotic pressure of one isosmotic
solution, for instance, of a sugar solution, by an
osmometric contrivance, we may transfer this
value to the osmotic pressure in the cells. So it was
found that the osmotic pressure in cells is equiva-
lent to five and more atmospheres, one atmosphere
being equivalent to about 0-3 per cent of salt-
petre.

The action of polioplasma on the growth of
living cells consequently consists in the production
of substances which generate osmotic pressure.
We know that only such substances as do not pene-
trate the protoplasmatic layer are capable of pro-
ducing osmotic effects. It is very little known
what substances having that effect are generally
produced by plant cells. It is seemingly highly
complex acids related to sugar which participate
in generating turgor effects in living cells. Intro-
ductory to the process of growth a certain amount
of turgor pressure is indispensable. We have to
assume that by that pressure protoplasm as well
as the cell wall is thinned and first stretched, then
new particles of cell wall substance are inserted,
57

CHEMICAL PHENOMENA IN LIFE

by which process the expansion of the cell wall
becomes permanent.

The most striking feature of cell life is the
fact that an enormous number of chemical re-
actions take place within the narrowest space.
Most plant cells do not exceed o-i to 0-5
millimetres in diameter. Their greatest volume
therefore can only be an eighth of a cubic milli-
metre. Nevertheless, in this minute space we
notice in every stage of cell life a considerable
number of chemical reactions which are carried on
contemporaneously, without one disturbing the
other in the slightest degree. How can we explain
this striking phenomenon ? In the first place we
must state that polioplasm is highly specialised
in its different parts. Besides the nucleus, which
certainly is the seat of most important vital
activities, we find many organs which are to be
recognised with the aid of the microscope as
distinct protoplasmatic organs, and we already
know the functions of many of them. Most plant
cells contain clearly differentiated small bodies of
different shape which are employed in the service
of the assimilation of sugar and carbohydrates.
In common plants they are green in colour, and
possess the remarkable power of absorbing carbon
dioxide, if bright light is admitted, and of forming
sugar from the carbon dioxide and water. These
are the chlorophyll bodies or Chloroplasts. Very
little is as yet known about their detailed structure.
58

CYTOPLASM AND NUCLEUS

In my laboratory it was lately shown that the con-
sistence of chloroplasts is often very soft, very
much less solid than the nucleus. They contain a
mixture of two kinds of colloids, one of them which
swells in water, of hydroid character, the other
resembles fats and most probably contains the
green 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 free
from colouring matter, and which form starch
from sugar. We call all these protoplasmatic
organs which are in the service of carbohydrate
metabolism, Plastids. As far as we know, they are
never formed from other plasmatic parts. They
always take their origin from mother plastids by
cleavage. In some plant cells there have been
found special plasmatic bodies which form fat,
but more frequently fat is independently formed
in the fundamental plasma substance. We may
say the same of the protein substances of proto-
plasm. It may be, however, that for the formation
of all these compounds very small centres or
distinct organs exist, which cannot yet be recog-
nised even by means of the highest microscopical
power. In any case, the parts where the different
chemical changes take place must be separated
in some way from each other, to prevent mixing
with other substances. In colloid systems, as such
separating walls, we find membranes formed of
59

CHEMICAL PHENOMENA IN LIFE

precipitated solid colloids or gels. From the small
size of these separated parts the whole protoplasm
must have the appearance of a foam formed by
gel walls, inclosing in its meshes colloids of more
liquid state. This hypothesis is not without
support from experiments. The eminent zoologist
Biitschli, of Heidelberg, has shown for many
colloids, both inorganic and organic, that they
have a foam-like structure which may be in some
cases observed through the microscope. Evidently
such foam-like structure in protoplasm must
facilitate the great variety of chemical processes
carried on contemporaneously in the narrow field
of a microscopical living cell.

These structures can be transitory as well
as permanent. It is very probable that in the
course of evolution the former gave origin to the
latter. A problem of great interest is the question
of the nucleus. We know that the lowest organ-
isms, such as Bacteria and the blue-green algae
called Cyanophyceae, do not contain a typical
nucleus. In the Protozoa the nuclei are in many
cases of much more primitive structure than in
higher animals. In the highly organised plants
and animals the structure of the nucleus is so
intricate, as is seen particularly in the process
of the cleavage of nuclei, that the problem of
nuclear structure cannot be longer considered
a chemical one. The nucleus rather acts as a
special organism in the cell. To a certain
60

CYTOPLASM AND NUCLEUS

degree plastids may be spoken of in the same
way.

But the bulk of Cytoplasma shows clearly by its
vital phenomena that it is principally transitory
structures such as are found in other colloids,
that occur there. A well-known fact is the
streaming of protoplasm. Streams of liquid
colloid matter wander in continual movement
through the different parts of the cell, carrying
with them different bodies, very frequently the
chloroplasts, and in some cases even the nucleus
itself. Very little is known about the reason for
this remarkable phenomenon. The general im-
pression is that surface tension plays a great part
in such plasmatic streaming. By continual change
of the chemical properties of the plasmatic surface
phenomena may result such as are seen in stream-
ing protoplasm. In any case, permanent structure
cannot be given in freely streaming protoplasm
which is continually moving in different parts
of the cell. Nevertheless, numerous chemical
changes of the greatest importance must take
place in the streaming polioplasma under the
same conditions which are found in other colloids.
Just in this territory the chemistry of Life may
hope to obtain results of the widest significance.

61

CHAPTER VI

CHEMICAL REACTIONS IN LIVING
MATTER

NE of the chief characteristics of living matter
is found in the continuous range of chemical
reactions which take place between living cells
and their inorganic surroundings. Without cease
certain substances are taken up and disappear in
the endless round of chemical reactions in the
cell. Other substances which have been pro-
duced by the chemical reactions in living matter
pass out of the cell and reappear in inorganic
nature as waste products of the life process.
The whole complex of these chemical transforma-
tions is generally called Metabolism. Inorganic
matter contrasts strikingly with living substance.
However long a crystal or a piece of metal is kept
in observation, there is no change of the substance,
and the molecules remain the same and in the
same number. For living matter the continuous
change of substances is an indispensable condition
of existence. To stop the supply of food material
for a certain time is sufficient to cause a serious
lesion of the life process or even the death of the
cell. But the same happens when we hinder the
passing out of the products of chemical transforma-
62

REACTIONS IN LIVING MATTER

tion from the cell. On the other hand, we may
keep a crystal of lifeless matter in a glass tube
carefully shut up from all exchange of substance
with the external world for as many years as we
like. The existence of this crystal will continue
without end and without change of any of its
properties. There is no known living organism
which could remain in a dry resting state for an
infinitely long period of time. The longest lived
are perhaps the spores of mosses which can exist
in a dry state more than a hundred years. As a
rule the seeds of higher plants show their vital
power already weakened after ten years ; most of
them do not germinate if kept more than twenty to
thirty years. These experiences lead to the opinion
that, even dry seeds and spores of lower plants
in their period of rest of vegetation continue the
processes of metabolism to a certain degree. This
supposition is confirmed by the fact that a very
slight respiration and production of carbonic acid
can be proved when the seeds contain a small
percentage of water. It seems as if life were
weakened in these plant organs to a quite im-
perceptible degree, but never, not even tempo-
rarily, really suspended.

Life is, therefore, quite inseparable from
chemical reactions, and on the whole what we
call life is nothing else but a complex of in-
numerable chemical reactions in the living sub-
stance which we call protoplasm. It must be

63

CHEMICAL PHENOMENA IN LIFE

one of the chief tasks in explaining chemical
phenomena in life to study the different chemical
reactions which take place in living protoplasm.

Chemists working with lifeless material have
as a rule to cause reactions by experiment, since
the material does not undergo any change by
itself. Comparatively few substances are readily
affected by the water and oxygen contained
in the surrounding air, without the help of the
experimenter. The biologist, on the contrary,
may watch numerous chemical reactions which
take place in living matter without his aid. It
is, however, difficult to study chemical reactions
in life in that way, because the single results cannot
be distinguished or separated from each other.
Results by far more exact are obtained when in an
experiment we bring together the living organism
with a certain substance to see what reactions are
caused. So we may watch the favourable or
unfavourable influence of this substance on the
living cells as well as the chemical transformation of
this substance by the living organism, when we
later on subject the organism to chemical analysis
or when we examine the products excreted by the
living cells. A great number of most valuable
results were obtained by such methods. Especially
the gradual change of substances taken up into
living cells by different reactions may be well
studied in that way.

The next step is to learn what kind of chemical
64

REACTIONS IN LIVING MATTER

means are available in living cells to produce such
results. We have now to bring together the sub-
stance which we had examined in its reactions in
living cells with other substances in vitro. So we
see whether analogous influences may be exerted
by some substances contained in cells or not.
We compare the artificial reaction outside the
organism with the vital reactions, and are enabled
to draw conclusions from our experiment for the
chemical reactions in living protoplasm. Striking
parallelism and resemblance are observed.

Such results, however, are incomplete, and
have been obtained only with certain groups of
substances. During the last decades biochemists
have more and more aimed at the study of the
total complex of the living cell after its death in
its reactions to certain substances. The earliest
experiments employed macerated tissue or whole
cells of microbes under conditions which prevented
decomposition by living bacteria. Salkowski
twenty-five years ago allowed yeast to stand with
water and some chloroform, that he might study
the post-mortem transformation in this deposit of
cells. It. was shown that many of the contents
of the living yeast cell undergo great change
under such conditions, and new substances were
found as products of such chemical reactions.
Such chemical transformation in dead cells where
microbial decomposition is excluded, is called
Autolysis. Of late very ingenious autolytical
F 65

CHEMICAL PHENOMENA IN LIFE

methods have been discovered. Instead of chloro-
form as an antiseptic toluol is generally used,
which liquid has scarcely any injurious effect
upon the substances of the cell. But, as Palladin,
of St. Petersburg, has lately shown that even the
grinding down does harm to many vital reactions,
it is better to kill the living tissues by freezing
and not to grind them. After having been frozen
at 20 degrees, and having been placed in a glass
with some toluol, the organs are brought back
into room temperature. It is said that under such
conditions more reaction takes place than when
the material is ground down.

We owe to Edward Buchner, of Wiirzburg,
another remarkable method which has the ad-
vantage of permitting us to work with liquids
without any particles of living cells, as in auto-
lytical methods must otherwise always be done.
Buchner recommends the material being ground
down as finely as possible, and quartz sand or
silicious marl being added. The thick paste of
cells and silicious powder is then pressed out in an
hydraulic press under a pressure of 300 to 500
atmospheres. In this way all the cell sap is
separated from the solid parts of the cells, and
contains but a very small quantity of cell frag-
ments. Even these may be removed by filtering
through a Chamberland candle filter. The clear
cell sap, however, still contains many substances
which were hitherto known only in living intact
66

REACTIONS IN LIVING MATTER

cells. Macfadyan and Rowland proposed a very
good amendment of this method. The living
organs 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 of
cells is ready for autolytic experiments. These
methods, highly developed as they are, are con-
tinually increasing in number and value. A con-
siderable number of reactions are now separable
from general cell life, and these reactions may be
studied isolated from life. Such is the aim of
modern biochemistry.

Chemical reactions are bound by certain con-
ditions. They may by some means be accelerated
or diminished. The chief influences we meet with
in the chemical laboratory are temperature,
physical condition, separating and mixing.

Chemists are always ready to boil a test when
they desire to accelerate the dissolution or reaction
of a substance. It is a matter of common know-
ledge that chemical reactions are considerably
hastened by a higher temperature. It is true
that plants as a rule do not show a higher tempera-
ture than the temperature of the surrounding air.
But there are remarkable exceptions. Bacteria
have been found in rotting hay and other decom-
posing plant material and also fungi, which pro-
duce a very high degree of heat even as much
as 60 degrees. Similar results were obtained with
67

CHEMICAL PHENOMENA IN LIFE

leaves which were kept in a chest carefully isolated
to prevent loss of warmth. We may consider that
heat is generally produced by plants, just in the
same way as by warm-blooded vertebrates. But
there are no contrivances in plants to keep the
temperature at a certain point above the tempera-
ture level of their surroundings. From numerous
experiments we learn that plants are in their vital
functions adapted to a certain average tempera-
ture. Not a few tropical plants suffer from frost
and even die when the outside temperature falls
below four degrees above zero. At the same
temperature, on the other hand, many alpine
and arctic plants have to perform all their functions
in life. In tropical plants the fat of the seeds melts
as a rule at a temperature of 30 to 40 degrees. It is
solid at the ordinary room temperature of 15
degrees. European plants always show the melting-
point of their fat not far above zero. Daily
observation teaches us that plant life develops
considerably more quickly in a higher temperature.
Growth, respiration, and the assimilation of carbon
dioxide, as well as the phenomena of movement
and stimulation, reach a much higher velocity
and power in a temperature of 30 to 35 degrees
than in one below 20, and by far higher than in a
temperature below 10 degrees.

The eminent Dutch chemist Jacobus Hendricus
Van 't Hoff discovered the rule that chemical
reactions are influenced by temperature with the
68

REACTIONS IN LIVING MATTER

result that the velocity of reaction is doubled or
trebled when the temperature increases by 10
degrees. This rule, well known to the chemists
of our days as Van 't Hoff's Rule or the R.G.T.-
Rule, is in practice applicable between the ex-
tremes of - 50 and 300 degrees. Below and above
these extremes the quotient is larger than 3 or
smaller than 2. It is of great interest to see that
chemical reactions in plants strictly follow the
same rule. F. F. Blackman and Miss Matthaei
showed that the dependence of the carbon-
assimilation of leaves in sunlight upon the tem-
perature is an exact example of Van 't Hoff's Rule.
Blackman stated the same for the respiration of
plants. Kanitz drew attention to many former
observations of different authors which demon-
strate quite sufficiently that the R.G.T.-Rule is avail-
able for protoplasma-streaming, geotropism, longi-
tudinal growth, pulsation of vacuoles in cells, etc.

As well as the influence of temperature on
chemical reactions, the influence of the physical
condition of the reacting substances is an old
laboratory experience : Corpora non agunt nisi
fluida. The chemist is accustomed to dissolve
the substance which is to be used in an experiment
to react on other substances. The chemical course
in living cells is the same. All substances destined
for reactions are first dissolved. No compound is
taken up into living cells before it has been dis-
solved. So the mineral salts of soil, the organic
69

CHEMICAL PHENOMENA IN LIFE

compounds when being digested by the leaves of
Drosera or by parasitic fungi are dissolved before
they enter further chemical reactions in the living
cells. Digesting is essentially identical with dis-
solving, or bringing into a liquid state. On the
other hand, the chemist knows how to save a
substance from chemical change by reactions, by
transferring it from the state of solution into a
solid state. This is what is called precipitation.
The solid insoluble deposit of the substance now
remains chemically unchanged. Metabolism in
plants employs the same means. Substances
which are to be stored up, such as starch, fat,
or protein bodies, are deposited in insoluble solid
form, ready to be dissolved and used whenever
wanted for the life process. Further substances
which are useless or even poisonous are easily
withdrawn from the complex of chemical reactions
in living protoplasm, and form a solid insoluble
deposit. For instance, oxalic acid is a wide-
spread product of oxidation in living cells which
has strong poisonous properties. Oxalic acid
immediately forms an insoluble compound when
calcium salts are present. In reality deposits of
oxalate of calcium are most common in plant
cells. We may then maintain that oxalic acid
is in this way withdrawn from active metabolism.
Resins and essential oils in quite a similar manner
are isolated and separated from the other reacting
substances in living protoplasm.
70

REACTIONS IN LIVING MATTER

To separate substances from each other by
filtration or by shaking with suitable liquids is one
of the daily tasks of the chemist. We must
expect analogous processes to occur regularly
in living cells. When nitrations are to be quickly
finished, we have to use filters which have a large
surface. In living protoplasm this condition is
very well fulfilled by the foam-like structure, which
affords an immense surface in a very small space.
We have been told that fine membranes form the
meshes of the network in protoplasm. These
membranes have the function of filters. We know
already that they are not permeable for every
substance. On the contrary they dissolve and let
certain substances pass through, whilst others
are retained. In this way a most perfect separation
is reached which may be compared with our best
filtering contrivances. I may add that by ad-
sorption the plasma membranes retain numerous
substances, which process is quite analogous to
precipitation and elimination from other reactions.

Finally, we have to mention the importance of
procedures of mixing in chemical reactions. In
ordinary laboratory practice mixing is carried
out by stirring. In living cells there could not be
any better contrivance for stirring or mixing than
the streaming of protoplasm. There are many
considerations which render it very probable that
the real purpose and use of the streaming of proto-
plasm is the performing of this function.
71

CHAPTER VII
VELOCITY OF REACTIONS IN LIVING CELLS

/'"CHEMICAL reactions are very frequently
V_x practically completed at the same moment
at * which they begin. It is quite impossible to
measure the time which elapses from the moment
when the reacting substances are brought in
contact up to the moment when the end of the
reaction is reached. When solutions of nitrate
of silver and of sodium chloride are mixed, the
two solutions immediately form the well-known
white, flaky precipitate, and, provided that there
is enough nitrate of silver present, all the chlorine
is deposited in the form of insoluble silver salt.
Most reactions used in analytic Chemistry are
reactions of enormously great velocity. We
comprehend, therefore, why chemists did not turn
their attention to the laws of Reaction Velocity
till in the last decades, when organic synthesis
continually taught that there are many chemical
reactions which require a considerable length of
time before being ended.

Most reactions in Inorganic Chemistry take
place between electrolytes — substances which are
good conductors of electric currents. Many
72

VELOCITY OF REACTIONS

reasons are brought forward in favour of a view
which Faraday had first expressed, to explain
the conducting of electric currents. The molecules
of electrolytes are split, to a greater or less extent,
into smaller particles which are called Ions.
These ions carry the electricity from one pole to
the other. They may be considered, as physicists
believe, to be compounded of atoms and a certain
quantity of electricity. The number of molecules
split into ions depends upon the degree of dilution
and the temperature. Strong acids and alkalis
are practically entirely split up into ions when
they are diluted down to o-ooi of one gramm
molecule in one litre of water.

The reactions which such substances undergo
may be considered as reactions between ions.
We generally call them Ionic Reactions. We shall
bear in mind that ionic reactions are carried out
with infinitely great velocity. The quantity of
ions contained in a solution can be calculated
by determining its power of conducting electric
currents. The less resistance is offered the more
ions are present. The sap of living tissues always
contains different ions. Therefore ionic reactions
must always take place in living protoplasm.

Ionic reactions in living cells did not fail to
attract much attention amongst biologists. We
possess a series of excellent methods for deter-
mining the concentration of ions contained in
living cells. Some of them permit us to work with

73

CHEMICAL PHENOMENA IN LIFE

extremely small quantities of material. Especi-
ally useful are the cryoscopic methods which allow
us to determine the number of ions in the volume
unit from the depression of the freezing-point in
comparison with that of pure water. The chief
source of ions for plants is the moisture of
the soil taken up by the roots. It contains,
in a very diluted state, salts of sodium, potas-
sium, lime, magnesium, iron, also hydrochloric,
sulphuric and phosphoric acid. Practically only
ions of .these substances pass into the living
plant cells. Some of these ions must dis-
appear in reactions Very quickly. Thus in
living cells we cannot find potassium in the well-
known reactions with platinum chloride. Traces
of potassium salts immediately furnish the yellow
deposit of platinum potassium chloride, but this
result cannot possibly be obtained in living cells.
When we burn the tissue to ashes and try the
reaction again, success is certain. We may
draw the conclusion that potassium salts are prob-
ably transformed in living cells into non-ionic
compounds of potassium.

Very important is the formation of Complex
Ions in metabolism. Iron salts, for example, are
certainly not present in living protoplasm, but the
presence of iron is always easily shown in plant
ash. We can see what kind of transformation
may be taking place from the reaction of copper
sulphate in the presence of organic compounds.
74

VELOCITY OF REACTIONS

Sulphate of copper is immediately precipitated by
potassium hydroxide as a light blue gelatinous de-
posit of hydroxide of copper. When we add sugar
solution, or solution of sodium tartrate, this deposit
is dissolved into a dark blue liquid. This liquid no
longer shows the characteristics of solutions which
contain simple ionic copper. Therefore copper
ions cannot be present. Those present are com-
pound ions containing both copper and the organic
substance.

Similar processes are, as we know,, common
in living cells. But living cells can even form
new ions from non-ionic substances. When
oxalic acid is formed from sugar or protein
matter, new ions of this strong acid come into
existence. Many other cases of the production
of ions from non-electrolytes in living cells could
be mentioned. When reactions between ions
take place in protoplasm, they are not carried out
in a watery liquid medium, but in a colloidal
medium. It is a question, however, whether the
Reaction Velocity is the same as in water. Ex-
perimental work of the last years does not leave
any doubt that a colloidal medium diminishes the
velocity of chemical reactions as well as the diffu-
sion of dissolved substances. Thus it is certain
that colloids of firmer consistence, such as solid
gels, must retard the course of chemical reactions,
even of ions. In spite of this, ionic reactions are
completed in an immeasurably short time, and
75

CHEMICAL PHENOMENA IN LIFE

practically the influence of the viscous colloidal
medium in protoplasm is of very little importance
for ionic reactions in living cells.

The most important substances among the
carbon compounds of living matter are not
electrolytes. Neither sugar, fatty bodies, carbo-
hydrates, nor protein bodies conduct the electric
current but to a very slight extent. All these
substances, then, which form the greater mass of
living protoplasm are non-electrolytes, and in
watery solution will only form a very small
quantity of ions or no ions at all. Most of the
chemical reactions which take place in assimilation,
digestion, and excretion are connected with such
non-electrolyte organic compounds. It is, therefore,
of interest to learn how great the velocity of such
reactions is in comparison with ionic reactions.
It is very easily shown that reactions between
molecular solutions are carried out comparatively
slowly, especially when the temperature does not
exceed 20 degrees. So it is when starch is trans-
formed into sugar, or protein into amino-acids,
that there is no difficulty in measuring the velocity
of chemical reactions. Such experimental work is
very important to obtain an exact theory of the
different chemical processes in living protoplasm.
We define as Reaction Velocity the quantity of the
substance transformed, measured in gramm mole-
cules per litre, which disappears in the unit of
time, viz. in one minute. If there is only one
76

VELOCITY OF REACTIONS

substance transformed at the same time in the
mixture of reacting substances, and if, therefore,
the concentration of only this substance varies,
whilst the other substances remain unchanged,
the mathematical law of the process is quite simply
found. The velocity of such a reaction must
directly depend throughout the reaction on the
acting quantity of the substance. Since this
acting quantity of the substance is constantly de-
creasing, we see that the velocity of the reaction
cannot remain the same. It must diminish in a
certain ratio. Suppose 20 parts out of 100 are
transformed in the first minute, then there remain
in the second minute only 80 parts :
100—100x0-2=80.

We find for the process in the third minute the

same : 0 0 _

80—80x0-2=64

In the fourth minute :

64—64x0-2=51-2, etc.

When we introduce for 100, which is the concentra-
tion at the beginning of the reaction, the general
symbol C0, and for 80, 64, 51-2, etc., subsequently
Cp C2, C3, . . : Ct, and for the constant factor
0-2 the symbol k, the equations are :

CQ-CQk=C1 or C0 (i-k)=C1
further —

C0(i-k)-CQk (i-k)=C2
or C0 (i— &)2=C2

77

CHEMICAL PHENOMENA IN LIFE

further —

C0 (i-£)3=C3
finally —

C0 (i-k)'=Ct.

If, instead of I, we take the time unit equal to
£, we have to take k w-times smaller, and, in-
stead of /, to write nt. The equation will now be :

C/T *\«/ c
o I1—) — k,,,.

If we introduce for £ the value ldt we have for
n=kd. The equation then becomes :

r /_ i\<<*/ r
co (1—3) =<s*t.

The expression (i— j)rf can be developed
according to the binomial theorem into e, the
basis of natural logarithms. The equation can be
formed as follows :

C.x^'=Cn,
Or if we take logarithms :

In CQ—ln Ct=kt.
By introducing Brigg's logarithms we have :

*i =0-4343* =7 (log CQ-log Q.

This expression contains values which may be
determined by experiment. If we therefore find
that the quotient of the difference of the logarithms
in the beginning and at the end of the time of
observation, measuring the time in minutes, is
constant, we may be certain that only the con-
78

VELOCITY OF REACTIONS

centration of one substance was changed. Such
reactions are called Reactions of the First Order, or
Monomolecular Reactions. Most of the reactions
which take place in living cells seem to belong
to this order. The determination of the substance
still remaining can be made in different ways.
Very often polarimetric control of the liquid in
which the reaction takes place allows of a very
exact conclusion on the rate at which the substance
disappears. The refraction of light, or even a
change in colour, can be used as a reagent of the
chemical process.

In other cases the law of the reaction is a different
one. We find that the reaction velocity is not
directly proportional to the quantity of the
reacting substance, but proportional to the square
of this quantity. In all such cases, two substances
are simultaneously changed in their concentration.
Such a process takes place in the decomposition of
esters, the compounds of organic acids and
alcohols, under the influence of an alkali. There
the concentration of the compound is continuously
diminishing. But, on the other hand, the con-
centration of the alkali, which is used up in the
formation of the alkali salt of the organic acid, also
decreases. So it is, for instance, in the reaction
between sodium hydroxide and ethyl acetate :

CH8-C2H6OOC+N*OH =
N0OOC-CH3+C2H5OH.

79

CHEMICAL PHENOMENA IN LIFE

Such reactions are called Bimolecular Reactions
or Reactions of the Second Order. Many reactions
in living cells follow the law of these reactions.
Reactions of a higher order are not as yet known
from living cells. We may at least be certain
that the great majority of all reactions in living
matter are not connected with the chemical
change of more than two different substances.

In molecular reactions we generally meet with
the peculiarity that the reaction is not quite com-
pleted when the reaction velocity has reached the
value of 0. A certain quantity of the original
substance always remains and never disappears.
Molecular reactions are consequently incomplete.
Thus a small quantity of cane sugar remains un-
changed when cane sugar is split by means of
diluted hydrochloric acid, and in the same way
some quantity of the unsplit ester remains when we
split it by means of acid into alcohol and acid.
This remarkable phenomenon becomes quite clear
if we suppose that the two reactions always take
place in opposite directions. Simultaneously with
splitting up begins the synthetical reaction, and
synthesis increases in proportion as the splitting
of the compound advances. The velocity of the
splitting process decreases at the same rate as the
velocity of the recomposing process increases.
At a certain time both processes have the same
velocity. No further change takes place in the
chemical system, provided that nothing is taken
<. So

VELOCITY OF REACTIONS

away nor added. The characteristic stage of
equilibrium of the reaction has been reached.
We express this rule by writing the chemical
equation connected by a double arrow instead of
the sign of equation :

C2H5OH + CH3COOH ^± C2H5OOC-CH3+H2O

Ethyl alcohol + Acetic acid^I^ Ethyl acetate + Water

or C6H1206+C6H1206 ^± C12H22On+H2O

Glucose + Fructose ~^~^[ Saccharose + Water

This theory involves the condition that all these
reactions may be reversed under certain circum-
stances. It only depends upon the external con-
ditions in which direction the situation of the
stage of equilibrium is displaced, either [in the
direction of composition or in the direction of
decomposition. We may draw the further con-
clusion that many chemical processes in living cells
may obey this kind of law. Under certain circum-
stances cells may contain more grape sugar and
fructose, under other circumstances more cane
sugar. Only chemical or physical agents influence
this relation, and we need no longer take refuge
in mysterious " vital forces " when we want to
explain these facts. Just such chemical reaction-
complexes occur most frequently in living cells.
The digestion and dissolution of organic matter in
the cell on the one hand, and the storage of organic
matter on the other, must be ruled by analogous
G 81

CHEMICAL PHENOMENA IN LIFE

laws. When there is a scarcity of food, the diges-
tion of starch or protein must yet be continued
until the concentration of the disintegration-
products has reached a decisive point. But
has the concentration risen above a certain point,
the process of recomposition becomes predominant,
with the result that storage of starch or protein
takes place.

Such regularity can only exist as long as no
reaction products are taken away or added. When
we remove the products of dissimilation, e.g. the
sugar produced in the decomposition of starch,
the splitting process continues and does not cease
until the whole stock of starcli has disappeared
and has been transformed into sugar. Working
upon this principle we can deprive seeds entirely
of starch, even the isolated endosperm when the
embryo has been removed. The seeds are fastened
each upon a small cylinder made of plaster of
Paris, which is placed in a dish filled with water.
The principle of such an experiment is quite the
same as that which is followed in the emptying
of leaves of starch during the night. In the process
of respiration and growth at night the growing
plant consumes considerable quantities of sugar.
At the end of a warm summer day leaves are full
of starch, and allow a constant stream of sugar
solution to be directed to the places where sugar
is consumed. By this process the decomposition
of starch grains is continually assisted, since all
82

VELOCITY OF REACTIONS

the sugar which has been formed from starch is
immediately removed.

The contrary effect, viz. that further formation
of compounds is hindered when the storage of this
compound has reached a certain stage, is also a
frequent phenomenon in living organisms. When
leaves are cut off from the branch and are exposed
to sunlight under favourable conditions of life,
for a certain time they continue their assimilation
of carbon dioxide, and starch is formed to a con-
siderable extent. Even more starch is stored in
such leaves than in normal leaves which have not
been separated from the plant. But, after a time,
carbon dioxide assimilation diminishes and ceases
entirely. The concentration of sugar in the leaf
cells.becom.es too great and the assimilation process
is hindered by the reaction products.

The mechanism accelerating and ceasing re-
actions in living cells is very often simply regulated
by the general laws of reaction velocity, and we
need not assume any special power of living proto-
plasm. The next chapter will touch on one of the
most important influences on the reaction velocity,
and will show that living cells possess most effective
means to accelerate reactions and to cause sur-
prising chemical results.

CHAPTER VIII
CATALYSIS AND THE ENZYMES

IN the beginning of the last century chemists
made the acquaintance of a series of re-
markable phenomena, which were caused by
finely divided metals, particularly by platinum in
the form of the so-called Platinum black. A
mixture of oxygen and hydrogen immediately
explodes when it is brought in contact with
platinum black. Common coal gas inflames when
brought in contact with finely divided platinum.
Sulphur dioxide is by the same agency quickly
oxidised to sulphuric acid. Hydroperoxide is
rapidly split into oxygen and water when in
contact with platinum black. In all these cases
the quantity of platinum black is not diminished
after the reaction, and the products of the reactions
are never any of the platinum compounds. Similar
effects were later on known from sulphuric acid
in its influence on the formation of ethyl ether
or sulphuric ether from the common ethyl alcohol.
Here, too, no sulphuric compound is formed.
Ether is often called Sulphuric Ether for the
reason that it is prepared by means of sulphuric
84

CATALYSIS AND THE ENZYMES

C TT

acid. Its formula n ^ > O does not contain

L2H5

any sulphur. It is formed from alcohol simply by
loss of water: 2 (C2H5OH) - H2O = (C2H5)^ O.
No sulphuric acid is consumed in this process.
Such remarkable reactions have become known in
continually increasing number. Since the effect of
the metal or the sulphuric acid seems to be caused
merely by contact, the German chemist Mitscher-
lich proposed to call such effects Contact Effects.
Mitscherlich recognised a very important fact
in many of such contact reactions, viz. that in
these the large surface of finely divided contact
substances must play an important part. The
famous Swedish chemist Berzelius, who took a
great interest in these phenomena, believed that a
peculiar force is exerted by contact substances.
He called that force Catalytic Power. The name
Catalysis has since been generally accepted. Cata-
lytic reactions soon became most important for
biology. Just a century ago Kirchhoff, of St.
Petersburg, found that starch is transformed into
grape sugar by the working of mineral acids.
It was known to him that no acid is consumed in
this process. In 1833 Payen and Persoz in Paris
made the discovery, which has had far-reaching
consequences, that germinating seeds contain a
peculiar contact substance, which transforms
starch into sugar. This substance they named
Diastase. In quick succession similar reaction
85

CHEMICAL PHENOMENA IN LIFE

effects were recognised in the formation of prussic
acid from the so-called amygdaline in germinating
bitter almonds, in the formation of the sharp
essential oil in germinating mustard seed, and,
finally, in protein digestion in the stomach of man
and the higher animals. Berzelius did not hesitate
to express his opinion that catalytic reactions
will probably one day represent the most im-
portant part of the chemistry of living cells.

At present, indeed, we have at our disposal a
surprisingly great mass of facts which illustrate
the general occurrence of catalytic substances in
living cells and the overwhelming importance of
catalytic reactions for chemical phenomena in life.
I shall try to explain the position of our knowledge
in the following pages as well as it is possible to
do in a narrow space.

To Ostwald, of Leipzig, we owe a very ingenious
and practical definition of catalytic reactions and
catalytic power. Substances which act as Cata-
lysers, as we now call them, usually exert their
influence upon a suitable substance, even when
applied in very small quantities. As a rule one
part of the effective substance may transform
many thousands, even millions of parts of the
substance undergoing the catalytic change. But
during the reaction the quantity of the catalyser
does not diminish. For instance, when splitting
up cane sugar into glucose and fructose by means
of acid, the acidity of the solution does not show
86

CATALYSIS AND THE ENZYMES

the slightest alteration. Finally, as we have al-
ready seen, no trace of the catalyser appears in
the final products of the reaction. Reactions
which show these characteristics we call Catalytic
Reactions. The enormous power of the slightest
trace of a catalytic substance strongly reminds the
biologist of the effects of stimulation in animals
and plants. Even here a slight stimulus very often
produces a surprisingly great effect. Physiologists
know that there is as a rule no mathematical
relation between the energy of the stimulus and the
energy which becomes manifest in the reaction.
For such physiological phenomena the expression
Release Action was used. Pfeffer tried to compare
such processes with the mechanism of a machine
which may be set working by touching an electric
button or a spring. Indeed, in both cases the
releasing action is not at all comparable with the
resulting action. May catalytic effects also be
called release actions ? Physiologists sometimes
did so, but there is no doubt that there are reasons
enough for drawing an exact distinction between
the two results. When the trigger of a gun is
touched, it does not matter whether more or less
power is applied. The energy produced by the
explosion is always the same. In catalytic re-
actions, on the other hand, the quantity of the
catalyser employed is of great importance as
regards the amount of the reaction effect. Between
certain limits one may even consider the reaction
87

CHEMICAL PHENOMENA IN LIFE

effect as proportional to the quantity of the
catalysing substance. So the acceleration of the
splitting of cane sugar by acids was found to be
directly proportional to the concentration of
the acid applied. Another difference is shown by
the experience that release effects in processes
of stimulation in plants or in animals do not occur
without a stimulus. But catalytic reactions, as
it seems, are not strictly dependent for their
existence on the presence of the catalyser. For a
series of reactions it has already been stated
that the reaction takes place even without the
catalyser being present, yet, it must be admitted,
slowly.

We come to the conclusion that the catalysing
substance is only an accelerating agent, but not
an agent without which the effect does not take
place at all. This is very important for an exact
understanding of catalysis effects. If we find
it desirable to compare the catalyser with any
mechanism in an engine, we cannot compare it
with a releasing contrivance, but we may rather
find a resemblance between the effect of train-oil on
the smooth going of the engine and the accelerating
effect of a catalysing substance.

Hitherto only accelerating catalysis has been
spoken of. Some effects on chemical reactions
have been found which seem to have the contrary
of an accelerating catalytic influence. The oxi-
dation of sulphurous acid, for example, can be
88

CATALYSIS AND THE ENZYMES

very much retarded by traces of glycerin, mannitol,
or other organic compounds. The luminosity of
phosphorus is diminished or hindered by the
presence of turpentine, ether, or alcohol. Prob-
ably all such influences are based in the working
of these agencies on a catalysing substance. In
the first case which we have mentioned, traces of
copper contained in the common distilled water
of our laboratories exert a catalysing influence
upon the oxidation of the sulphite of sodium.
Organic substances, for example mannitol and
glycerin, are inclined to form compounds of copper
and so they remove the effective catalytic agent
from the water, and diminish the velocity of the
oxidation of the sulphite of sodium.

We owe to Bredig, of Zurich, the exact knowledge
of the retarding influence of traces of prussic acid,
sulphide of hydrogen and some other substances
on the catalytic reaction of platinum black and
hydrogen peroxide. There is no doubt that
prussic acid or hydrogen sulphide change the
surface of the platinum, for they cover it with a
layer of platinum cyanide or sulphide. So the
platinum surface which exercises the catalytic
power is very considerably diminished. By
decomposition of the cyanide layer the pure plati-
num surface can be restored and the catalyser
becomes active again. There is an interesting
parallelism between these phenomena and the
poisoning of living cells by cyanide or sulphide,
89

CHEMICAL PHENOMENA IN LIFE

which made Bredig call such retarding substances
Poisons for catalytic and enzyme effects.

A very interesting result in chemical reactions
is often given by the phenomenon that the cata-
lysing substance is formed by the reaction itself.
Pure copper metal is very much less soluble in
quite pure nitric acid than in nitric acid which
contains a little nitrous acid. The latter acid has
a catalytic influence on the process of the dissolving
of copper. Now some small quantity of nitrous
acid is always formed by the reduction of the
nitric acid during the process of dissolving copper.
We therefore see that, after a certain time, the
copper dissolves much more quickly than in the
beginning. Such a catalysis is called A utocatalysis.
We may compare it to the influence of heat on the
dissolution of sodium hydroxide, during which
process 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 quite
usual catalytic substances which affect nearly
every kind of reaction.

It is a very important fact that the final equi-
librium in the reaction is as little altered by the
presence of the catalysing substance as that the
order of- the reaction is changed. Consequently
the catalytic influence does not extend but to the
reaction velocity. Catalytic reactions are of the
greatest importance for chemical phenomena in
90

CATALYSIS AND THE ENZYMES

living matter. We may even say that all the main
reactions in the different processes of digestion,
in respiration, in the metabolism of carbo-
hydrates, fats and proteids are ruled by catalytic
influences. No chapter of biochemistry during
the last period of development in biology has
become of greater significance than the theory
of catalysis in living protoplasm, or the knowledge
of the Enzymes.

The word Enzyme has not been used until re-
cently. Formerly the expression Ferment was
generally applied to signify the cause of the
remarkable chemical changes which are so highly
characteristic of life. Ferment or Fermentation
was directly derived from alcoholic fermentation.
The word was intended to signify the generation
of gas, of foam bubbles filled with gas, and it should
remind us of the resemblance to boiling liquids :
ferveo, boil, bubble. Figuratively, fermentation
was applied to chemical changes in organic bodies
under organic influences. There was no marked
distinction made between fermentation and rotting
or decomposition. Generally fermentation and
putrefaction were spoken of as being the same.
The first great discovery in the territory of fermen-
tation was made by Theodore Schwann in Belgium
and Cagniard Latour in France. It was shown
that the deposit consisting of yeast in fermenting
sugar solution was of vegetable nature, not a
product of fermentation as was formerly often
91

CHEMICAL PHENOMENA IN LIFE

believed, and that it was the active cause of the
fermenting. From that time yeast has been placed
in the plant system among the fungi. A little later
Kutzing was able to show that the cause of acetic
fermentation was also a microscopic plant, be-
longing to the bacteria. It is still well remembered
what great services Louis Pasteur rendered to the
knowledge of microbes which cause different
fermentations. In consequence of these dis-
coveries the name of ferments was transferred to
the microbes causing fermentation. I have
already taken the opportunity of mentioning a
further wonderful discovery of the remarkable
third decade of the last century. I mean the
isolation from germinating seeds of a substance
which is able to transform starch into sugar.
Payen and Persoz first showed that extract of
malt contained a certain substance, soluble in
water, and which was precipitated by alcohol,
which causes the starch grains to dissolve and
induces the formation of sugar from starch. The
two French scientists even showed that this sub-
stance, to which was given the name of Diastase,
immediately loses its power when boiled. Theo-
dore Schwann, at about the same time, discovered
that from the mucous membrane of the stomach
there can be extracted a substance which is soluble
in water or glycerine, and which acts very effec-
tively upon albuminous compounds, quite in the
same 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 of
Emulsin, which splits up the amygdalin contained
in almonds to prussic acid, benzaldehyde and
grape sugar ; the discovery of Myrosin in mustard
seeds, which produces mustard oil ; later on the
discovery of Invertin in yeast, which cane sugar
splits into its sugar components ; Trypsin in the
pancreas gland of quadrupeds, which rapidly
splits up albumin to amino-acids. Many other
discoveries were made later on, in connection
with which I only mention the important state-
ment of Schoenbein in Basel, that oxidising effects
are caused by substances which are soluble in
water, precipitated by alcohol and destroyed by
boiling. All these substances exercise their
activity, even when applied in very small quan-
tities. They are all of organic origin, never found
in inorganic nature, and not to be gained by
chemical synthesis. We do not wonder that such
effects caused by diastase and the other sub-
stances mentioned were not sharply distinguished
from the microbial processes of fermentation or
decomposition. We indeed see the expression
Fermentation used for both kinds of phenomena.
It was found sufficient to speak of Soluble Ferments
and of Microbic Ferments.

Kuhne, of Heidelberg, was the first to propose to
change the nomenclature and to avoid speaking of
ferments. He clearly recognised that even the
93

CHEMICAL PHENOMENA IN LIFE

microbes cannot act otherwise but by production
of substances which must be regarded as Soluble
Ferments. Consequently the name of Enzymes
was introduced for soluble ferments. We know
that all enzymatic processes depend upon the
production of such substances. All the processes
which were formerly believed to be exclusively
connected with living protoplasm are due to
substances of the group of Enzymes.

In this direction, particularly the discovery of
Edward Buchner, of Wiirzburg, then in Munich,
was of the greatest importance. It was shown
in 1894 that the power of fermenting sugar in yeast
is by no means inseparably connected with cell-life.
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 a
powerful hydraulic press, a yellowish liquid is
obtained which still possesses the full property
of forming alcohol and carbon dioxide from grape
sugar. Buchner succeeded by nitration in freeing
this liquid from every trace of living cells or their
fragments, so that there could not be any doubt
that no living protoplasm was present. Further,
he demonstrated that the alcohol- forming agent
was soluble in water, precipitable by alcohol, and
very easily destroyed by heat. So alcoholic
fermentation was separated from yeast-life and
the perspective was opened, that many other
processes of decomposition or disintegration of
94

CATALYSIS AND THE ENZYMES

substances in living protoplasm may be caused
by enzymes, but not directly by the living matter
itself.

But it is true that in some cases substances
which are responsible for enzymatic actions cannot
be extracted from protoplasm. The expressed
sap proves ineffective and no means are known
for separating the hypothetical enzyme from the
protoplasm. In such cases it is, however, possible
to kill the protoplasm without destroying the
enzymes. Here, too, Buchner was the first to
show useful methods. He succeeded in killing
cells by means of acetone or ether without damag-
ing the enzyme. So killed yeast-cells were ob-
tained which possessed in a high degree the power
of acting on sugar. In the same way Buchner
prepared the bacteria of milk fermentation and
of acetic fermentation. The cell-bodies were com-
pletely dead, but nevertheless it was possible to
cause fermentations by specimens of these bacteria.
We may consider that such experiments fairly
prove the existence of specific enzymes which are
responsible for the fermentation effects by the
living cells. It is difficult to explain the reason
why the enzymes in these cases cannot be separated
from protoplasm. They may be entirely insoluble,
or may at least diffuse through membranes only
with difficulty, or adsorption effects may play a
part in such cases.

Investigations of later years have shown dis-

95

CHEMICAL PHENOMENA IN LIFE

tinctly that every cell contains such enzymes
which are not to be extracted from protoplasm,
and which never diffuse from intact living cells.
Such enzymes were named Intracellular Enzymes
or Endo-Enzymes. Other enzymes, such as the
cane sugar inverting enzyme of yeast, or the
digestive enzyme of the mucous membrane of the
stomach are abundantly secreted and conse-
quently may be obtained without difficulty in
any quantity from living tissue. These are the
enzymes which we call Secretion Enzymes.

We understand that chemists were very anxious
to isolate pure enzymes and to study the pro-
perties of these most remarkable substances in
the hope of being able to explain why they act in
that way. In spite of the very advanced technical
achievements of experimental chemistry, it was
not possible to prepare a pure enzyme, not even
in one case. The difficulties of preparation are
very great. All enzymes have proved to be
typically colloidal substances, and they readily
show alterations of 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, so
that the chemist, in his endeavour to separate
the effective agent from its companions, loses
more 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

CATALYSIS AND THE ENZYMES

less activity than the original enzyme. We must
confess that it is at present impossible to say
Whether all enzymes belong to ihe class of al-
buminous substances, as in many cases seems
probable, or whether enzymes may be of different
chemical structure. It is not even certain whether
all enzymes contain nitrogen.

As far as we know all enzymes are distinctly
colloidal substances. No enzyme survives boiling
even for a short time. Although there is great
uncertainty about the chemical nature and
relation of enzymes we possess much knowledge
of the action of enzymes, which is doubtless the
most interesting part of their characteristics.
At the first glance we must feel reminded of
catalytic reactions. Berzelius made no difference
between enzymes and catalytic substances. As
well as being catalysers the enzymes show strong
actions even when applied in but very small
quantities. It was stated with regard to a series
of enzyme reactions that the quantity of the
enzyme is not diminished in a perceptible degree
during the reaction. We know further that the
enzyme never appears among the products of a
reaction, quite as in catalytic reactions. Finally,
it is most probable that the reactions which are
caused by enzymes do not entirely depend for their
existence upon the presence of the enzyme. They
are continued and take place, though very slowly,
even when the enzyme is not present. We see that
H 97

CHEMICAL PHENOMENA IN LIFE

the chief characteristics of catalytic substances and
of enzymes agree exactly. We must in consequence
of 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 about
extend their sphere of action over a large number
of substances. Acids, for example, are able to
catalyse all kinds of reactions. Quite a different
behaviour is met with in enzymes. As a rule
enzymes are effective only in one reaction. In-
vertin does not act upon anything else but on
cane sugar, emulsin only upon amygdalin. Their
sphere is, as we see, very limited. Another pecu-
liarity of enzymes is their colloidal nature and their
inability to resist boiling temperature. There is
little doubt that both properties are connected,
and that the sensibility to heat is due to coagula-
tion of colloidal solutions. We may therefore say
that enzymes are catalytic substances of a limited
field of action, of colloidal nature, and very little
resistent to heat. We must still add that enzymes
are formed only in living matter. Finally, one
important property of enzymes is this, that in the
blood of animals which have had some enzyme
solution injected into a vein, peculiar substances
are formed. These have the power of hindering
the enzyme action when a little of the blood serum
is added to a mixture of the original enzyme
solution and the substance on which the enzyme
98

CATALYSIS AND THE ENZYMES

is otherwise effective. We call these remteikable
substances Anti-Enzymes. Only real enzymes
cause the formation of anti-enzymes in animal
blood, and this reaction is highly characteristic
of true enzymes. It is important to know that
each anti-enzyme acts quite specifically only upon
that enzyme which was injected into the vein,
and upon no other.

Enzymes are as a rule easily soluble in water, in
salt solutions, or in glycerine, but yet some are
known which are scarcely soluble in water, such as
the fat-splitting enzymes and that which acts upon
malt sugar. They pass slowly through animal
membranes. Adsorption phenomena are very
marked in enzymes. All are greedily taken up by
coal or by flakes of blood-fibrin. We prepare
enzymes roughly from watery solutions by pre-
cipitating with alcohol. Sometimes they may
be extracted with glycerine. In a somewhat purer
state they are obtained by precipitation with a
strong salt-solution, particularly when repeatedly
precipitated. When they cannot be dissolved in
water, the cells are ground down carefully and
some toluol is added to the paste. Such toluol
preparations show most of the reactions of the
endo-enzymes. It is true that toluol autolysis is
not free from disadvantages.

As a rule the cell-paste is effective on a great
number of substances. A paste prepared from
root-tips is able to split up starch and cane sugar,
99

CHEMICAL PHENOMENA IN LIFE

as well as albuminous bodies ; it acts on oxidisable
substances and splits up fats. The same \vas
found of paste formed from animal liver. Most
probably a large number of different enzymes
occur in the narrow space of each cell. It is
astonishing to see how all these actions can be
exerted at the same time without disturbing each
other and how exactly regulated they are. We
have here another argument for the subtle struc-
ture which protoplasm must possess, that every
substance of the cell is kept in its proper place,
and cannot mix with the others. It is an im-
portant fact that enzymes of a certain kind are
not formed by the organism under all conditions.
That was shown distinctly in experiments on
moulds. The common mould, Penicillium glaucum,
when cultivated on starchy material produces in
abundance an enzyme which acts on starch, the
so-called Amylase or Diastase. But if the fungus
is kept on starch-free food, it has been found that
it does not contain any diastatic enzyme. The
latter is only immediately and abundantly pro-
duced when starch is added to the culture medium.
Penicillium even produces an enzyme which acts
on wood substance, as I once showed. But such an
enzyme is only produced if the fungus is cultivated
on wood and not upon any other substance. We
must conclude that the formation of enzymes in
the organism underlies some regulations, and that
it is a purposive process in life.
100

CATALYSIS AND THE ENZYME'S

Now comes the question what enzymes may
be formed of. Very little has hitherto been dis-
covered about the origin of enzymes. Only a few
hints are given by a series of experimental results.
In a number of cases it has been stated that
extracts from cells do not contain ready and
effective enzymes. But when they are treated
with very diluted acetic acid or other milder
chemical agents they begin to show distinct
working on fat or albuminous matter or on starch.
Therefore the supposition was arrived at that the
fresh cell-extract contained the natural mother-
substance of these enzymes, and that this mother-
substance was able to furnish the enzyme itself
by artificial transformation. The original sub-
stances were called Pro-Enzymes or Zymogens.

Studies on the pancreatic ferment in animal
intestines have shown that the fresh pancreatic
juice does not act on protein bodies. But when it
is brought together with the intestinal liquid it
begins to act most energetically on proteins. The
intestinal liquid entirely loses its activating effect
when boiled. The activating substance must
consequently be destroyed by heat .quite as
enzymes are. Other experiments showed that
the activating substance of the intestinal sap
much resembles a true enzyme, and it may be
called an Enzyme activating Enzyme, or Kinase.

Enzyme effects are assisted also by many other
substances. We know the great influence which
101

CHEMICAL PHENOMENA IN LIFE

is exercised on the protein-splitting enzyme
of the stomach-secretion by hydrochloric acid or
another acid in sufficient concentration. Many of
the enzymes of plant cells are favourably influenced
in their action by acids quite in the same way.
The pancreatic enzyme on the other hand shows
a contrary behaviour. It is supported by diluted
alkaline solutions. Very remarkable is the
activating effect on the fat-splitting enzyme of the
pancreatic gland exerted by the organic acids
of bile, the glycocholic and taurocholic acid.

Such activating effects are extremely widely
spread in the part which enzymes play in the life-
process. One sees how these enzyme effects may
be regulated, strengthened, and weakened, as
the effects are required.

Many chemical substances hinder enzyme
reactions in a most characteristic manner. Stronger
acids or stronger alkalis generally diminish the
enzyme effects as also alcohol, formaldehyde,
cyanide of potassium, aromatic substances, and
many inorganic substances, such as the salts of
heavy metals, iodine, sulphurous acid, etc. Such
a paralysing influence is not only exercised by
these substances, but the living cell is able to
produce special substances, which are destroyed
by heat, which are effective in very small quanti-
ties, and which paralyse enzyme reactions. We
have spoken of these already as the Anti-Enzymes.
Anti- enzymes are doubtless produced in the
102

CATALYSIS AND THE ENZYMES

normal metabolism of plants and animals. I
found a very interesting case of an anti-enzyme
in root- tips after geo tropic stimulation. This
anti-enzyme acts on oxidising enzymes, and is
able to reduce their effect considerably. Quite
distinct is the specific nature of anti-enzymes.
The anti-enzyme of geotropically stimulated roots
of maize does not alter the anti-enzyme effects
of oxidising enzymes from the bean or sunflower.
On the other hand, the anti-enzyme of the bean-
root acts on the enzyme of other leguminous plants
only. The specific nature of anti-enzymes is met
with in a similar way in the animal anti-enzymes
which are produced in the blood when enzymes
are injected into the venous system. As we have
already mentioned, anti-enzymes are formed under
such conditions, which paralyse only the enzyme
which was injected, and no other.

Just as a high temperature has a great influence
upon the velocity of reactions catalysed by sub-
stances of inanimate nature, the enzyme reactions
are likewise considerably accelerated, when the
temperature is raised. Van 't HofFs Rule seems
to be followed even in enzymes. The reaction
velocity is doubled or trebled when the tem-
perature is raised by 10 degrees. But it is true
that this rule is only found for certain intervals
of temperature. Besides its accelerating effect
on the velocity of the enzyme reaction, a higher
temperature strongly influences the velocity of the
103

CHEMICAL PHENOMENA IN LIFE

disintegration of the enzyme. The higher the
temperature the more unstable are enzymes.
At a temperature of over 60 degrees enzymes are
rapidly decomposed, many become immediately
inactive when they are heated up to 63 to 65 degrees
Celsius. We therefore understand that there
probably exists a certain temperature at which
the enzyme work is best done, viz. one at which the
accelerating effect of the temperature is strong
enough to finish the reaction very quickly, and
where 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 two
curves. The line AB shows the acceleration of
the enzyme reaction by the rising temperature.
We take it for granted that this influence is directly
proportional to the temperature. The curve CD
shows the destruction of the enzyme by the
temperature rising. This influence as far as we
know is not simply proportional to the temperature.
Suppose the quantity of the enzyme at o is 100,
and the quantity at 70 degrees is o, we have to
draw the curve CD. So we recognise that the
optimum of the effect lies between 50 and 60
degrees. Only about 55 per cent is active, but
the strong acceleration of the reaction velocity
neutralises 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

CATALYSIS AND THE ENZYMES

and the resulting curve of the enzyme effecjt
slightly approaches the axis of abscissas. At a
higher temperature the quantity of the active
enzyme decreases rapidly, and so does the re-
sulting effect, which becomes o at 70 degrees.

90
80
70
CO
SO
, 40
30
20
fO

!O 20 SO 40 JO 60 70 80 9O tOO'C

Such superposition of two curves causes the
culmination of the resulting curve in E. In prac-
tice it is not advisable to use too high a temperature
for enzyme reactions. A medium temperature is
in most cases the best. We shall not be surprised
to see that this so-called Optimum of enzyme
reactions coincides with the temperature which
is most favourable for the life process. F. Frost
Blackman, in a series of most interesting papers,
showed that the dependence of different life
105

CHEMICAL PHENOMENA IN LIFE

processes on the temperature obeys a similar
rule to that of enzyme reactions. Whenever we
find an Optimum of a certain vital function at a
certain temperature we must think of the crossing
of two kinds of influences. One of these in-
fluences is the accelerating effect of the tem-
perature on chemical reactions, the other the
destructive effect of higher temperature on the
active substances of living cells. We only have
to add that most of these active substances belong
to the enzymes.

It is important that the equilibrium of Enzyme
reactions is not altered by temperature. Van 't
Hoff has explained this fact. Enzyme reactions
cause neither a great production nor a great con-
sumption of heat. All reactions of such character,
of a comparatively small caloric change are not
affected in their equilibrium by temperature.
Therefore the constant of equilibrium in enzyme
reactions 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 in-
juriously on all enzymes hitherto examined.

Very interesting relations exist between the con-
centration of the enzyme solution and the enzyme
effect. We have related that many catalytic
reactions follow the law of monomolecular reac-
tions. So, for example, the destruction of hydrogen
peroxide by platinum sol, or the splitting up of cane
io5

CATALYSIS AND THE ENZYMES

sugar by diluted sulphuric acid, are reactions of the
first order. In every moment of the reaction
its velocity is directly proportional to the quantity
of the substance yet unchanged, and directly
proportional to the concentration of the acid.

Quite similar ratios were found in enzyme
chemistry. The cane-sugar-splitting enzyme of
yeast, called Invertase, and Amylase or the starch-
dissolving agent in seeds, act in the same way. Be-
tween certain extreme limits the effect is directly
proportional to the concentration of the enzyme.
So it is possible to calculate the quantity of
invertase or of amylase in a solution, when a
standard solution of the same enzyme is used.
Pepsin of the stomach showed a different result.
In Prague, in 1885, Schutz discovered that the
amount of protein digested in a certain time
is not proportional to the quantity of the enzyme
itself, but proportional to the square root of the
quantity of the enzyme. This rule has often been
confirmed. But it was only a couple of years ago
that Arrhenius, of Stockholm, explained this
remarkable law. If we consider that the deter-
mination of the enzyme effects is made in the
first stage of the enzyme action, we may assume
that the quantity of the transformed albumin
is very small in comparison with the quantity
of the albumin not yet decomposed. We can
therefore suppose that at the beginning of the
reaction the quantity yet unaltered is constant.
107

CHEMICAL PHENOMENA IN LIFE

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-lj-(i).

According to the rule of Schutz, the ratio of the
transformed albumin x to the time wanted for the
transformation is —

or x = '.
If we differentiate, we find

2X'dx=kl-dt or ^ = *-f-?.
dt 2 x

As long as M is proportional to the reaction
velocity (i) Schutz' rule must therefore be valid.
Another question is whether even enzyme
reactions are of the first order, that is, are mono-
molecular reactions or not. We see that the
question is of great importance. In the case of the
enzyme reaction being really of the first order, we
know that only one substance in its concentration
is altered during the reaction. And that cannot
be any other than the substance on which the
enzyme is acting. Consequently the enzyme con-
centration itself remains constant. In this way we
obtain the proof for the identity of enzyme re-
actions and catalytic reactions. As early as 1890
excellent papers were published by O'Sullivan and
Thompson on the reaction between cane sugar
and invertase. These authors came to the conclu-
108

CATALYSIS AND THE ENZYMES

sion that the reaction follows the law of monomole-
cular reactions. This theory was by no means
generally accepted. French and German scientists
of great weight denied that the law of the reaction
is simply the law of mass effect, and empiric
formulas were calculated which sufficiently agreed
with the course of reaction observed. It is to
Hudson that we owre the proof that O'Sullivan
and his collaborator were quite right. The
able American chemist found that the chief
mistakes in such investigations are caused by the
circumstance that grape sugar continually changes
its action on polarised light when just split off
from cane sugar. This property of glucose is
called mutarotation. Hudson very cleverly avoided
this source of error by adding some alkali to the
solution before the polarimetric determination
was made. Thus the state of equilibrium is at once
reached in the rotation and the determinations
of glucose can be made without any difficulty
and with full certainty. In this way it was clearly
shown that the inversion of cane-sugar by invertase
is just as much a monomolecular reaction as the
parallel reaction of cane-sugar inversion by means
of acid. Investigations were made on fat-splitting
enzymes which showed the same law, but the
results of others were different. But another
enzyme very clearly follows the law mentioned
above. That is the catalase, which splits up
hydrogen into water and oxygen. Finally the
109

CHEMICAL PHENOMENA IN LIFE

tyrosin oxidising enzyme of plant cells was
found to follow the law of monomolecular re-
actions. Even if we do not yet possess clear
knowledge about other important enzyme re-
actions, these results are most remarkable. Hope
is given us that some more enzyme reactions are
quite identical in their mechanism with catalytic
monomolecular reactions. Since we have seen
that Schutz' Rule can be simply explained, and is
by no means peculiar to enzyme reactions, we
believe that it is very probable that enzymes are
nothing else but organic catalytic substances
without any peculiar property. Complications,
it is true, are frequently produced by the colloidal
properties of enzymes, which cause the great
instability of the enzymes. In most cases the
quantity of the enzyme is diminished at the end
of the reaction because of the destruction of a
certain amount of enzyme in other reactions
which occur besides the main reaction. • It is
easily understood that this must lead to important
differences from the law of monomolecular re-
actions.

Finally we have to touch on the question of the
specific character of the different enzymes. A
priori we do not know whether one and the same
enzyme cannot catalyse different reactions. But
many reasons can be given for the supposition
that by far the greater number of the enzymes
act upon only one substance. Although most
no

CATALYSIS AND THE ENZYMES

living cells show different enzyme effects, we
find a certain variety in their combinations,
and never find two or more enzyme effects in-
separably connected in any case. So in germinating
seeds we very often observe catalytic effects
both on cane sugar and on malt sugar. In other
cases these two effects are strictly limited to two
different cell-species. In yeast Saccharomyces
cerevisia acts very effectively on cane sugar, but
not on malt sugar, whilst Saccharomyces Marxi-
anus only acts on malt sugar. When we prepare
a watery extract from both species of yeast we
can easily convince ourselves that even there only
one of the two enzyme effects is exerted. By
Marxianus only the splitting of maltose, by
Cerevisice of saccharose. We cannot doubt that
these two enzymes are different substances.
Many more difficulties arise when the enzymes
cannot be separated from the cells and the enzyme
effects are watched only in the paste of ground-
down cells. There it is often impossible to say
to what number of enzymes all these effects should
be attributed. All in all one feels at present in-
clined to indulge in the opinion that each single
effect corresponds to one certain enzyme. We are
justified in doing so, since many enzyme prepara-
tions have in the course of time proved to be
mixtures of different enzymes. It was well known
that preparations of starch-attacking enzymes gave
in most cases a blue reaction with guaiacum resin,
in

CHEMICAL PHENOMENA IN LIFE

Then amylases have been met with which did
not show this guaiacum reaction. Finally extracts
were obtained from plants which only gave the
guaiacum reaction but did not act upon starch.
So the conviction was arrived at that the blue
reaction 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 the
system of the enzymes upon the kind of reaction
which each carries out. Thus the nomenclature of
enzymes nowadays is generally taken from the
enzyme action. It was found convenient to
compose the name of the enzyme with the ending
-ase, taken from the first described and isolated
enzyme, 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 we
shall call starch - decomposing enzymes, from
amylum, starch, Amylase ; similarly the enzyme
acting on cane sugar Saccharase, etc.

The chemical characteristic of the enzyme
reaction or the special decomposition caused by
the enzyme is very different. In many cases the
action 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

112

CATALYSIS AND THE ENZYMES

united in the chemical group of Hydrolytic Enzymes
or Hydrolases. Among these enzymes different
sub-orders may be distinguished according to the
chemical order to which the substance attacked
belongs. If esters or compound ethers of alcohols
and acids are decomposed by enzymes the latter
may be called Esterases ; if they act on carbo-
hydrates, Carbohydrases ; if they act on fats,
Lipases, etc.

Other enzymes have the peculiarity that they
split off the group NH2 from nitrogen containing
organic substance. Since this group is called the
Amido-group, the enzymes must be named
Amidases. To such enzymes belong even the
most important enzymes which act on proteids,
the Proteases. Certain enzymes produce precipita-
tions in albuminous solutions by hydrolysis. We
call them Coagulases.

Another group is characterised by the oxidising
effects of its enzymes. These are the Oxidases.
Their counterpart is formed by the Reductases, or
reducing enzymes. Further are known enzymes,
which split off carbonic acid from organic acids.
We call them Carboxylases. Perhaps even the
enzyme which causes the alcoholic fermentation
by yeast, the Zymase, belongs to these.

For physiologists it is rather more interesting to
distribute the enzymes according to their physio-
logical significance in the living cell. Following
the physiological principle, we may distinguish
i 113

CHEMICAL PHENOMENA IN LIFE

three large groups of enzymes : enzymes in the
service of the assimilation of food and of digestion,
enzymes employed in respiration, and those
employed in dissimilating processes partly forming
the so-called end-products of metabolism. We
may maintain that all decomposing processes
connected with the assimilation of food are ruled by
enzyme reactions. The end of all these reactions
is to form from the substances occurring in food
the primitive stem-substance, such as glucose
from the carbohydrates or amino-acids from
albuminous substances. Each cell contains such
enzymes, and is able to reconstruct its substances
from the fundamental organic groups which are
formed from the food by a host of enzyme re-
actions. In consequence of this, each cell is able
to rebuild its own specific albumin from the food,
and does not take up the albuminous substances
as they are present in the food without any change.
We therefore distinguish two stages in the digestion
and assimilation of food. One stage is merely
analytical, a splitting stage. Here the different
hydrolytic enzymes, such as Upases, amylase,
saccharase, maltase, the proteases, develop their
activity. In the following stage the reconstruction
of cell-substance takes place, the synthesis of
the organic principles of life. Modern chemistry
has been fortunate enough to obtain even here
remarkable results from experiments.
We should remember that hydrolytic processes

H4

CATALYSIS AND THE ENZYMES

such as the decomposition of esters are reversible,
and it only depends upon the conditions of the
experiment where the position of the state of
equilibrium is found : nearer to the ester or nearer
to the products of decomposition. Analysis and
synthesis are always connected. If a catalysing
influence acts on such reactions, it must accelerate
as well combination as decomposition. Else the
process would not agree with the fundamental
law of conservation of energy. We see that even
enzymes which catalyse a hydrolytic decomposi-
tion must act even in ..the contrary direction, as a
synthetical power. It was Van 't Hoff who first
stated this postulate. A short time afterwards
A. Croft Hill published his paper on the synthesis
of malt sugar by means of maltase, which had
hitherto been known only as a hydrolytic agent.
When maltase was made to act on a very concen-
trated solution of grape sugar, it was noticed
that a considerable quantity of a compound sugar
was formed from glucose. It is true that later on
it was shown that this sugar is not identical with
maltose, but consists chiefly of isomaltose, a closely
related sugar. Armstrong then showed that a
real synthesis of maltose can be made by means of
another enzyme, Emulsin, from grape sugar.
Emulsin is further effective on the synthesis of
the characteristic substance of bitter almonds,
amygdalin. When amygdalin is treated with
invertase, the cane - sugar - decomposing enzyme
"5

CHEMICAL PHENOMENA IN LIFE

of yeast, there are formed grape sugar and a com-
pound which is a combination of glucose and the
nitrile of amygdalic acid. Concentrated solutions
of glucose and the nitrilc-glucoside brought
together with emulsin form in abundance
amygdalin, the original glucosid of almonds, as
O. Emmerling has shown. Undoubtedly syn-
thetic 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 from
the enzyme which act on proteids. All these ex-
periences render it very probable that the organic
synthesis in cells is performed and regulated by
enzymes, and we can no longer consider the
formerly mysterious synthesis of organic com-
pounds in life as a problem which is not accessible
to chemical experimental investigation.

No less important prospects lie disclosed at
present relative to the part of enzymes in the
process of respiration. It was Lavoisier who
clearly recognised that the respiration of animals
was a process analogous to inorganic combustion.
About 1800 Saussure, of Geneva, during his
memorable investigations into plant nutrition
discovered the respiration of plants. Since that
time no doubt has existed that the fundamental
laws of the process of respiration are the same
in both the plant and the animal kingdom. It is
true that in plants and in the lower animals one
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CATALYSIS AND THE ENZYMES

characteristic is missing which most manifestly
directs our attention to respiration as a process of
combustion. It is the development of free caloric
energy. But it is not difficult to show by means of
suitable contrivances that each plant produces an
abundant quantity of heat in respiration. We
only have to keep germinating seeds in a Dewar-
glass for several days to show that the temperature
in the glass rises to 40 degrees and more. Careful
isolation therefore is sufficient to demonstrate
this production of heat. Physiological investiga-
tion taught that in both animals and plants the
materials of combustion are essentially the same.
Most frequently large quantities of fat, sugar, or
carbohydrates disappear during the process of
respiration. The striking feature in such chemical
processes in life is that these substances are not
used 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 respiration in a
fungus or in germinating seeds show what great
quantities of carbon dioxide are produced in a short
time, and how much sugar is consumed in respira-
tion. When we try to compare this vital decom-
position of sugar with the sugar-decomposing
processes which we apply in the laboratory, we
shall find it astonishing what effects are produced
in living cells without any high temperature, any
strong chemical reagent or electric current. A
M7

CHEMICAL PHENOMENA IN LIFE

lump of sugar may be exposed to the air for years
without showing more alteration than that it turns
slightly yellow. Thus we come to the conclusion
that organisms must possess special means which
produce the rapid decomposition of respiration
material.

The chemist Schoenbein, of Basel, was the first
to show that enzyme-like substances take part in
vital oxidation. He drew attention to the property
of many plant tissues of turning a colourless emul-
sion of resin of guaiacum in water blue. He then
showed that the effect on the guaiacum resin is
also found in the filtered watery extract of the
tissue, and that this oxidising effect cannot possibly
be obtained if the extract be boiled beforehand.
Later on numerous substances were found to be
such oxidising ferments. All plant and animal
cells contain such enzymes. But they act only on
aromatic substances, as phenols and resin acids ;
on sugar or on fat they do not show any effect.

The explanation of this fact came from the
discovery that pea-seeds, which are brought to
germination without access of air, produce a large
quantity of alcohol besides carbon dioxide. This
process, which is found widely spread in plants
which are kept without oxygen from the air,
proved to be fully identical with the alcoholic
fermentation of yeast. Even the enzyme which
Buchner had found in yeast and had called zymase
was stated to be present in higher plants. We
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CATALYSIS AND THE ENZYMES

must consequently believe that the primary de-
composition of sugar in plant respiration is closely
related to alcoholic fermentation, if not identical
with it. This is another type of respiration pro-
cesses in the living cell.

The aromatic substances on which oxidising
enzymes act seemed to have very little importance
for cell-life until Palladin, of St. Petersburg, whilst
working out experiments on plant respiration,
came to a remarkable hypothesis. Most of the
aromatic substances which are oxidised by the
enzymes furnish dark colouring matters as pro-
ducts of oxidation. This can be shown when killed
plants are kept in vapours of chloroform in an air-
tight glass vessel. Quite commonly they turn a
deep brown. Palladin supposes that such oxida-
tion processes take place even in living cells, but
the reduction of the colouring matters following
immediately, no staining becomes visible. The
aromatic substances therefore transfer the oxygen
of the air by means of oxidases to other oxidable
substances of the cell. This hypothesis explains
quite satisfactorily the existence of enzymes
which act only on aromatic substances, as well as
the position of the latter substances in the meta-
bolism of plants.

No small number of lower organisms are able

to live without a supply of air or free oxygen.

Pasteur discovered this important fact in yeast

and bacteria. Yeast may live as well without

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CHEMICAL PHENOMENA IN LIFE

as with oxygen, and with some bacteria it is
the same. For other microbes the presence
of air is deleterious, as they soon die when
brought in contact with a medium containing
even only small quantities of oxygen. The
possibility of life without oxygen can be shown
by the following experiment. A flask is filled
with a culture medium of sugar, pepton, and
Liebig's extract of meat. This liquid is sterilised
by boiling and infected with bacteria from tegu-
ments of bean-seeds. A quantity of soluble
indigo is added to stain the liquid dark blue.
Then the flask is well corked and allowed to remain
for one or two days in the incubator at 25 to 30
degrees Celsius. After this time we are sure to
see the liquid quite colourless, the soluble indigo
being reduced by the anaerobic bacteria which
develop rapidly and take the oxygen from the
indigo. When the bottle is reopened and its con-
tents poured slowly out into a dish, we see the
liquid immediately colouring greenish, then light
blue, and soon dark blue, as it was before. This
change is brought about by the reabsorption of
oxygen from the air. Such experiments show
distinctly that bacteria can grow without more
than minute traces of oxygen, and that under
such conditions the bacteria are able to draw
oxygen from its compounds by reduction. Different
results that have been arrived at lead to the con-
clusion that enzymes also take part in this process

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CATALYSIS AND THE ENZYMES

of reduction. These so-called Reductases seem
to 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 meta-
bolism as are no longer of any use for the organism.
They are removed from it as excretions, or form
in the tissue deposits which do not change. In
animal life a great quantity of nitrogenous sub-
stances are eliminated from the organism, as urea
and uric acid. It has been shown by several
authors that enzymes participate when these
excretion substances are formed. When the
bacteria which cause putrefaction of meat are
preparing their cell-substances from the proteins,
a number of atom-groups from protein are elimin-
ated as waste substances. Particularly when
putrefaction is going on without sufficient access
of air, many substances are formed which are
responsible for the peculiar smell of putrid matter,
and which are to be considered as bacterial excre-
tions. Such are some compounds of sulphur,
hydrogen sulphide itself, and methyl-mercaptan ;
further, indol and scatol are substances which are
very characteristic of putridity. No less must a
series of phenols be mentioned as products of
putrefaction. We have certain proofs for the view
that all these substances take their origin from
amino-acids, which are the primary products of
the decomposition of proteids. By splitting of
carbon dioxide and of ammonia the formation of

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CHEMICAL PHENOMENA IN LIFE

the substances mentioned above is easily explained,
and it becomes more and more probable that
enzyme reactions can cause these decompositions.
In the case of some of these enzyme reactions we
may be sure that they even occur in the cells of
higher plants and animals, and are not confined
to the lower organisms.

After our short review of the immensely ex-
tended territory of catalytic and enzymatic
phenomena in the living cell, we cannot but confess
that the importance of such processes is surprisingly
great. The large number of different chemical
reactions which take place in living protoplasm,
and which we know from physiology to be the
fundaments of chemical phenomena in life, is
comparatively well understood at present on the
basis of enzyme-chemistry.

It is true, there are some most important chemi-
cal processes in living cells which do not yet
form part of catalytic chemistry. I may here
mention the unique synthetical process in plants,
the formation of sugar from the carbonic acid of
the air by the chlorophyll bodies of green cells in
sunlight. But any day may bring the revelation
that even here catalytic phenomena are at work,
and nothing at present excludes the supposition
that enzyme effects take part also in these pheno-
mena of plant life. If we suppress our feelings
of satisfaction that Exact Science has been able
to penetrate into these mysteries of life, there are

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CATALYSIS AND THE ENZYMES

yet facts enough which show us how far we are
from a thorough understanding of the life-
process. The striking feature of the present state
of biological science is that nothing that we dis-
cover sufficiently explains the intimate connection,
the marvellous regulation of all processes in living
substance. Up to our days the living cell has
represented an unknown mechanism which reacts
most accurately and corresponds to the present
conditions and which possesses all abilities to
preserve its structure and the species beyond the
limits of life.

An exact knowledge of the chemistry and of
the physics of the living substance will un-
doubtedly teach us far more of these hidden
combinations than we know at present. I cannot
but add that there is nothing to indicate that the
phenomena of life are ruled by forces which are
different from chemical and physical energies in
inanimate Nature. The fundamental laws of
energetics seem to dominate in all Nature. The
two principles of the mechanic theory of heat
govern everywhere. In animate Nature no case is
known where the principle of Conservation of
Energy is not followed. The more exactly physio-
logical experimental work is carried out, the more
care is taken to apply quantitative methods.
Thus we have come into possession of a great
number of data which invariably show that the
transformation of energy obeys the same laws in

123

CHEMICAL PHENOMENA IN LIFE

life as in inanimate matter. In inanimate Nature,
further, we always meet with the important
phenomenon that caloric energy can never be
transferred from a colder body to a warmer one,
unless other special processes render it possible.
By itself heat can only be transferred from a
warmer to a colder body. This law, well known in
Lord Kelvin's utterance, that the energy present
in the world has the tendency to dissipate, doubt-
less governs living matter as well as non-living.
There is only one part of physiology which is not
yet accessible to our methods and which we cannot
prove to be ruled by the well-known laws of
inanimate Nature. These are the psychological
phenomena. At present we see no way to transfer
physical and chemical methods to the phenomena
of the psychical world.

124

CHAPTER IX

CHEMICAL ACTIONS ON PROTOPLASM
AND ITS COUNTER-ACTIONS

HITHERTO we know living protoplasm as a
complicated system of colloidal substances
possessing a highly developed structure, and ruled
by a great number of catalytic reactions. The
complex of these reactions is able to maintain the
cell-structure, to take up substances from outside
the cell to digest them and to gain from them
both energy and cell-substance for growth.

We have not yet completely treated of the
mutual chemical interchange between the outer
world and living cells. This influence consists in
something more than in taking up food and giving
off excretion substances. The whole life-process
depends to an enormous extent upon external
chemical influences. Minute traces of iron salts,
scarcely to be ascertained by chemical analysis,
possess the power of greatly accelerating growth
and respiration. Life can be destroyed by other
substances in quantities which are infinitely
smaller than the mass of protoplasm which the
deadly substance can injure. Such influences

CHEMICAL PHENOMENA IN LIFE

may be called Chemical Stimuli. Their action is
quite comparable to the action on living matter
of physical stimuli, such as light, warmth, elec-
tricity and gravity.

» It is quite a general rule that substances which
produce poisonous effects on living cells when
applied in a certain concentration, influence living
cells quite differently when their concentration is
more diluted. Then stimulating effects are
regularly produced. Respiration and growth
reach a higher degree than without application
of the poison. For example, potato plants treated
with copper sulphate show darker green leaves
and more vigorous stems than normal plants.
We see that poisonous action does not depend
only on the chemical nature of substances, but also
on the concentration of the substance. We should
rather speak of poisonous effects than of poisonous
substances. The explanation of the phenomena
may be given by the principle of action and counter-
action. The poison — for example, mercury chloride
or carbolic acid — develops a retarding influence on
some processes in living protoplasm. Protoplasm
is by this action incited to react against the
injuring influence. This is done by an acceleration
of the chief processes of life — respiration, growth,
and probably many others. So the toxic in-
fluence is paralysed. The successful counter-action
against the poisonous agent cannot, however,
take place when the toxic influence is too strong.
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CHEMICAL ACTIONS: PROTOPLASM

Then the latter prevails, and only the harmful
consequences become visible.

The discovery of further interesting chemical
stimuli was made in the course of the studies of the
consequences of extirpation of certain organs, as
the thyroid gland or the suprarenal bodies in
animals. This procedure invariably causes fatal
consequences for the organism. It is followed by
serious disturbances of the normal metabolism and
finally by death, so that there is no doubt that
these glands perform important functions. But
since the organs mentioned have no excretory duct,
the substances produced by them must be trans-
ferred directly into the circulation of the blood.
This internal secretion appears to be of the
greatest importance. Seemingly very different
substances are produced by these glands, not only
proteids, but also aromatic carbon compounds
have been stated to play a part in internal secre-
tion. But all these substances exert stimulating
and regulating effects on the organism. They are
generally united under the name of Hormones.
Even plants seem regularly to produce such
substances. The swelling of the ovary after
pollination is caused by certain soluble substances
of the pollen. Very likely the formation of flowers,
or of the sexual organs in lower plants, is con-
nected with the occurrence of Hormones in the
organism of plants.

Most remarkable chemical actions and counter-

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CHEMICAL PHENOMENA IN LIFE

actions are observed in living protoplasm when
other cells and their products, not only an inorganic
poison, are the injuring part. We may be reminded
of the interesting phenomenon with which we
became acquainted in the formation of anti-
enzymes. In the animal which has had an enzyme
solution injected into its veins, a substance is
formed which is able to hinder the action of this
but of no other enzyme. Such phenomena are
widely spread and are most important for the
study of chemical processes in cells. In studies on
pathogenic bacteria it has been shown that many
of them produce substances which are most
poisonous even in the smallest quantity, but differ
from other poisons by their albuminoid character
and their instability when heated. By boiling they
may be easily destroyed. Such poisons are formed
only by living cells. We call them Cytotoxins.
Such cytotoxins have become known not only
from 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, the
Jequirity plant, contain toxins of exceedingly
strong action. Cytotoxins, further, are found in
snakes, toads, the blood of the eel and some other
fish. If we consider the characteristics of cyto-
toxins we feel very much reminded of the proper-
ties of enzymes. The resemblance increases when
we learn that cytotoxins, quite in the same way as
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CHEMICAL ACTIONS : PROTOPLASM

the enzymes, cause the formation of specific anti-
substances when brought into the veins. The
formation of Antitoxins is quite analogous to the
formation of anti-enzymes. Antitoxins have the
specific effect of rendering the Cy to toxin, to which
they correspond, inefficacious. This Antitoxin-
phenomenon, as we know, plays an important
part in the defence of animal and human organisms
against the toxin-producing bacteria in infectious
diseases.

The production of anti-bodies is a most remark-
able feature in the mutual chemical influencing
of living cells against alien living cells and their
chemical products. Especially for pathology, the
study of such phenomena is at present of the
greatest importance. A whole new branch of
biochemistry, called Immunochemistry, has been
built up upon the basis of the general experiences
mentioned above.

In our general review of the chemical phenomena
in life we cannot but lightly touch on the facts
which show how the living organism protects itself
against the attacks of microbes. These facts are
very interesting for us to illustrate how the pro-
tective substances and the aggressive substances
of living cells may enter upon reactions. Cyto-
toxins, as well as enzymes, are typically colloidal
substances, and so are antitoxins. When anti-
toxins neutralise the cytotoxins we could think
that the cytotoxins would be destroyed. But it is
K 129

CHEMICAL PHENOMENA IN LIFE

not so. If we heat the mixture of antitoxin and
cytotoxin to nearly the temperature at which the
latter is destroyed by heat, we can reach a point
where the mixture again becomes toxic. We
get the impression that the antitoxin in the com-
pound has been sooner destroyed by heat than the
cytotoxin, and the latter has again become free and
effective. This most important experiment shows
us that both anti-substances enter into a com-
bination, analogous to that of chemical compounds.
Since we know that both substances are colloids,
we could suppose that colloid reactions are re-
sponsible for the phenomenon. Otherwise we
could think that the reaction is to be considered a
chemical combination of both substances. At
present there are many difficulties in the way of
giving a satisfactory explanation of the reaction.
Arrhenius drew a most instructive parallel between
the neutralisation of toxin and antitoxin, and the
neutralisation of a moderately strong alkali, such as
ammonia, with a weak acid, e.g. boric acid. Both
processes, indeed, have a great resemblance.
Ehrlich's ingenious hypothesis, well known as the
so-called Side Chain-Theory, culminates in the
supposition that the anti-substances represent
highly compound molecules with many atom-
groups, such as proteids possess. The neutralisa-
tion is done by binding two distinct groups. These
groups may be destroyed by heat, and both sub-
stances again set free. Possibly the two theories
130

CHEMICAL ACTIONS: PROTOPLASM

will one day be combined. The hypothesis of
Arrhenius is more satisfactory for the scientific
chemist. The theory of Ehrlich is founded upon a
sound atomistic basis, and has proved of great
heuristic value.

When toxin and antitoxin solutions are mixed,
no change can be seen in the solution. With other
anti-bodies it is quite different. It was found
that the blood serum of animals which had been
injected with bacteria of typhoid fever or cholera
asiatica gave a strong precipitate with the limpid
filtrate from cultures of the same bacteria. Even
this effect is quite specific. Further, it was shown
by a series of experiments that similar results are
obtained by injection of different proteids into the
venous system of animals. The blood serum is
then able to precipitate the proteid which was
injected, and exclusively this proteid, from its
solutions. All these reactions were called Pre-
cipitin Reactions. They are in many respects
most interesting. In the first place, they show
that comparatively primitive protein-bodies cause
the same anti-reaction as enzymes or cytotoxins.
But only protein-bodies are known to give the
reaction, no other organic compounds. When the
proteid is decomposed by pepsin and hydrochloric
acid the precipitin reaction cannot be obtained
again. The simple amino-acids which are formed
from protein in digestion do not give the precipitin
reaction. But the reaction is also satisfactorily

CHEMICAL PHENOMENA IN LIFE

obtained in albumoses and peptones, the most
primitive protein-bodies. There is every hope of
the possibility of soon explaining this reaction
much more exactly than is at present possible.

But even now we see what complicated reactions
can take place among proteids, and how easily
precipitates are formed without seriously changing
the original proteids. Most remarkable is the fact
that the proteids of a species of plant or animal
do not give any precipitin reaction with the blood
serum of an animal treated with the proteid of the
same plant or the same animal. Therefore the
reaction can be used to distinguish whether a pro-
teid is an alien one, or one belonging to a certain
species. Experiments were made by Uhlenhuth
on anthropoid apes, and on groups of lower apes.
Anthropoid serum from animals which were
treated with the blood of man does not give any
precipitin reaction. But serum from other apes
which were treated with the blood of man gives a
distinct reaction. We see from this fact that the
blood of anthropoids is not essentially different
from that of man. The proteids are the same in
both.

The result is that each species of organism
has its own specific proteids. We understand
now why the alien proteids which are taken in
with the food have to be split up until they finally
form amino-acids, so that the alien protein
structure is quite annihilated. Then the cells

CHEMICAL ACTIONS: PROTOPLASM

reconstruct the proteins according to the specific
structure of protein which is characteristic of the
particular species of organism. Further, we learn
from the experiments on precipitin reactions that
the morphological position of a species in the
system is also physiologically founded. We may
suppose that closely related species must also
show chemical relations. The chemical mechanism
of the precipitin reaction is not yet clear. We can
think of the phenomenon mentioned in a foregoing
chapter, that two colloids of contrary electric
charge flake each other out. Since albuminous
substances readily change the kind of electric
charge, many opportunities would be given
to cause such precipitate reactions. It has been
shown without doubt that the precipitin is entirely
consumed in the reaction. Therefore we cannot
state that any resemblance exists with enzyme
reactions. Living cells can even produce specific
substances having the properties of proteids
which have the power to agglutinate other cells
or unicellular organisms such as bacteria. A
similar effect is obtained by adding to a culture
of typhoid bacteria in the test-tube some of the
blood serum of an animal which had been pre-
viously treated with typhoid bacteria by in-
travenous injection. Flakes of bacteria are
formed, between them the liquid becomes quite
limpid, and the medium which had been turbid
with bacteria shows itself later on quite clear, and

CHEMICAL PHENOMENA IN LIFE

all the bacteria are found in the deposit. The
substance responsible for this reaction, the so-
called Agglutination of Bacteria, is destroyed by
heat and has the properties of a protein-body.
Substances of this kind we call Agglutinins. Even
this reaction is a strictly specific one. The
agglutinin produced by injection of a certain
species of bacteria gives to the blood serum the
specific agglutinating action on these bacteria.
Agglutination effects occur even in other toxins.
The toxin substance from the seeds of the castor
oil plant strongly agglutinates the red blood
cells, and so does the Jequirity toxin. There is no
doubt that the agglutinin acts on certain sub-
stances in the bacteria-cells or other agglutinable
cells. These substances are probably transformed
into a gelatinous state, which is seen in the clinging
together of the cells. The agglutinin is entirely con-
sumed in this reaction. It may therefore rather be
compared to a neutralisation than to an enzyme
action.

The most successful study of the alterations
which occur in the blood of animals, after in-
travenous injections of pathogenic bacteria and
their products, showed far more substances formed
which serve for the protection of the organism
than we have here mentioned. But all these
substances, such as opsonines, bacteriolysins,
and, further, the bacterial substances, such as
aggressines and others, which assist parasites
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CHEMICAL ACTIONS: PROTOPLASM

against their hosts, have hitherto not been of such
general biological interest that we need treat of
them.

This chapter had the purpose of showing that
numerous chemical influences are exercised upon
living protoplasm by the protein substances
of other cells, and that such reactions have a
markedly specific feature. The life process can
be stimulated or retarded by these influences,
production of certain substances can be pro-
voked or hindered, and death can even be caused
by such cell substances. We learned how far
the substantial specificity goes in an organism.
The structure in protoplasm is certainly not the
only characteristic which is decisive for living
substance. We have also continually to keep
in mind the chemical nature of the substances
in protoplasm.

Modern chemistry is not yet quite sufficiently
advanced to clear up this most interesting complex
of reactions between highly composed protein-
bodies. It is still the question whether the reac-
tions between toxins and their anti-bodies are
really of ordinary chemical character, or whether
they belong to the territory of colloidal reactions.
Here is one of the most suggestive problems
of modern Biology. There is no doubt that
enormous progress will come from further study
of Immunochemistry.

CHAPTER X

CHEMICAL ADAPTATION AND INHERITANCE

OUR review of the chemical phenomena in
life would not be complete unless we had a
last glance at the chemical phenomena of variation,
adaptation and inheritance in living beings. The
investigation of these phenomena lies at present
so much within the territory of morphology
that one scarcely thinks of the importance of
chemical work in this department of biological
science. Chemical methods, however, are here
of particularly great interest. Morphology, being a
comparative science, draws attention only to the
results of variation and adaptation. Chemistry
has to show the whole course of phenomena, not
only the results, and it has to consider the influence
of time on phenomena, to determine the minima
and maxima in the course of reactions, and to
introduce the Time Factor into all these in-
vestigations. In chemistry, therefore, variation
can be observed in the course of phenomena as well
as in the final results. Since alterations and
variations in the course of physiological actions
can generally be traced back to the influences of
136

CHEMICAL VARIATION

certain factors, chemical methods open up an
immensely wide outlook.

At present chemical investigations into variation
and inheritance unfortunately show so many gaps
that our report cannot be but a provisional one,
and it must rather contain suggestion for fresh
experimental work than material already worked
out.

The kinds of variations which morphologists
distinguish as' Fluctuating Variation and Mutation
are exactly repeated in the chemical properties
of living organisms. The Law of Fluctuating
Variation discovered by Quetelet is expressed
by the statement that the average values are the
most frequently recurring ones. The individuals
showing a certain characteristic more or less
marked, are rarer, the greater the divergence from
the average value or average size of the char-
acteristic. This law, which can so regularly be
shown by measuring the length, weight or volume
of an organ of plants or animals in a great number
of individuals, supplies exact returns in chemical
variations. De Vries gives a report of the result
of an examination of 40,000 sugar beets with
regard to their content of cane sugar. From the
curve given by De Vries we immediately recog-
nise the fundamental law. The average quantity
of about 16 per cent of sugar was found in nearly
7000 beetroots ; 12 per cent sugar in only 340
roots, 19 per cent in only 5. It is true that such
i37

CHEMICAL PHENOMENA IN LIFE

research work has not been carried out very often,
but the few experiments which have already
been made render it most probable that Quetelet's
law holds for chemical properties as well as for
morphological characteristics. It would be com-
paratively easy to examine the amount of acid
contained in leaves, the amount of starch or of
protein which is contained in one individual
in a great number of cases in order to confirm
the results mentioned above. No research work
at all has been done to determine the velocity of
chemical processes or reactions in a great number
of single individuals. Data without any difficulty
could be worked out on the velocity at which starch
or protein disappear from germinating seeds or on
the intensity of respiration in many individuals
which live under exactly the same conditions. It is
difficult 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 different
characteristics which are markedly inheritable.
Since De Vries' famous book on these phenomena,
we call such variations Mutations. Chemical
mutations are widely spread and well known. In
horticulture and agriculture many new mutations
which were kept on account of their valuable
chemical properties have in the course of time
been isolated. Fruits, containing an extraordinary

138

CHEMICAL MENDELISM

quantity of sugar, or of peculiar aroma and taste,
or corn containing a considerable quantity of
starch, are examples of such sudden chemical
variation. Doubtless to these chemical mutations
may be assigned all the results which were ob-
tained in morphological mutations. But even here
it is unknown whether mutations occur in the
velocity of reactions or vital processes in single
individuals, out of a great number of plants or
animals, and whether such variations are well
fixed and inheritable. Well worthy of exact
examination would be, further, the question how
chemical variation works in hybrids. It is well
known that the progeny obtained by crossing two
species of animals or plants, in many cases follow
the rule that only half the progeny remain of
hybrid character, but the other half return to the
parental types. This law is the famous Mendel's
Law. Up to our days we do not know whether
chemical characteristics may " mendel " too.
It is likely to be so in many cases, and could
without difficulty be confirmed at least in a
number of experiments. If chemical Mendelism
could be discovered, it would be of great interest,
because it lies in the nature of Mendelian char-
acteristics that they are based on qualities of the
nuclei of the sexual cells.

A further type of variation is known as Atavism.
In the formation of a certain characteristic some
individuals of the progeny return to the stage

CHEMICAL PHENOMENA IN LIFE

of this characteristic in the ancestors. There is
no doubt that chemical atavism will frequently
be found in connection with morphological
atavism. We need only think of the reappearing
characteristic of the uncultivated ancestors of our
fruit trees. But it is not yet known whether such
chemical atavisms can reappear without being
accompanied by morphological atavism.

Finally, we have to turn our attention to the
variations which are caused by external influences.
Botanists well know that the size and thickness of
leaves depend upon the intensity of the sunlight
in which they have grown. Especially the in-
tensity of light, but also the degree of moisture
in the air, gravity, mechanical and chemical
influences cause very remarkable alterations in
the morphological characteristics of plants. At
the same time chemical alterations must take
place, and we see at last from all the research work
which has been carried out in that domain, that
the variation is not merely a morphological one,
but is also chemical. One must feel it to be a great
gap in biological work that chemical properties in
their dependence on the physical and chemical
influences of their surroundings have not yet been
investigated for themselves alone. But a number
of facts show even now that chemical variation
depends on the influence of environment, and that
it shows a similar purposive tendency towards
adaptation to the environment, as is known in
140

CHEMICAL ADAPTATION

morphological characteristics and variations. The
oil-seeds of the plants of the flora of our country
always contain fat which is liquid at temperatures
of above 10 to 20 degrees Celsius, and becomes solid
at a few degrees above zero. Tropical plants very
frequently contain fat which melts only at a
temperature above 30 degrees, and is solid at an
average European temperature. This difference
is likely to be connected with the temperature
in which the plants live. Another phenomenon
of the same kind is the rule in the production of
enzymes. In moulds no amylolytic enzyme is
produced unless these fungi grow on culture
medium containing starch, and the common grey-
green mould Penicillium glaucum produces an
enzyme which destroys wood-substance, when it
grows upon wood, but never when it grows on
other substrata. For the formative action of
chemical and physical influences on the morpho-
logical qualities of organisms the term Morphoses
has been introduced. In an analogous manner
we can name the chemical alterations provoked
by these influences in plants and animals Chemoses.
Morphoses are to be considered as reactions of the
living organism to external stimuli. They belong
to the physiology of stimuli, and we cannot but
assume that they differ from tropisms and other
primitive forms of reactions only in their com-
plexity. Chemoses must be considered as reactions
of the living organism in the same way, and all
141

CHEMICAL PHENOMENA IN LIFE

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

Biologists are nowadays inclined to explain the
phenomena of adaptation in plants and animals
by the supposition that the hereditary adapted
forms took their origin from transitory morphoses,
which often do not last longer than the time during
which the external stimulus is acting on the
organism. In such a way may for instance be
understood the origin of dorsiventrality in plants.
A branch of ivy develops its rootlets only on the
shade-side, and turns its leaves all to the sun-side.
If we turn the branch by 180 degrees and fix it
in this new position, it changes its morphological
properties entirely, corresponding to the new
conditions. The old rootlets shrink and fall, but
new climbing roots are formed on the side which
is now turned away from the light. The dorsi-
ventrality is, as we see, not fixed. A branch of a
pine tree when turned by 180 degrees behaves
quite differently. The old part does not change
its character, and in spite of the unnatural position
the leaves remain without any reaction. But
when in the following spring the branch continues
its growth, the new part of the branch corresponds
in its formation exactly to the new position. We
see that a reaction could not be carried out in the
adult part of the branch, but the characteristics of
this part were not transferred to the new part.
The latter behaves according to its real life con-
142

CHEMICAL INHERITANCE

ditions. Again, the thallus of a liverwort, such as
Marchantia, shows differences. If a young gemma
of the moss is exposed to light in a certain position,
the lighted side is destined to be the upper surface
for ever, and the opposite side to be for ever the
root-producing under surface. Nothing can change
this. Such a case corresponds to adaptation, it is
strictly hereditary, and must be called a purposive
reaction, because the proper tissues develop on
both the light-side and the under surface.

We may be sure that thorough investigation of
chemical phenomena in life will certainly disclose
analogies. Most probably the self-steerage in the
production of enzymes belongs to a series of such
phenomena. On the other hand, the above-
mentioned formation in tropical plants of fats
of a high melting-point may be called a perfect
chemical adaptation.

Phenomena of inheritance of chemical properties
are as well known as those of hereditary mor-
phological properties. We know only how far
morphological and chemical properties are in-
heritable together, and how far chemical pro-
perties separately are hereditary. Nevertheless,
examples of chemical varieties show that some-
times only one chemical characteristic varies,
and no other. The bitter almond shows no
difference from the sweet variety of almond, but
by the presence of amygdalin. This case of
heredity depends upon fecundation processes,
143

CHEMICAL PHENOMENA IN LIFE

since the progeny of bitter or sweet almonds, re-
spectively, invariably show their peculiar char-
acteristic. Consequently the characteristic of
producing amygdalin depends on the nuclei of
the sexual cells. Generally, we speak of heredity
only when sexual processes are involved, and the
properties of one generation are transferred to the
following generations. In plants, however, it is
possible to take the conception of heredity in a
wider sense. Sensu stricto a sexual cell with its
properties is a part of the parental organism which
is separated from the latter and is beginning an
independent life. For heredity I think we must
not lay too much stress upon this circumstance,
and it does not matter whether the transferring of
parental properties takes place among cells which
remain connected or not. When in a growing
branch the young part acquires its properties from
the adult part, this process is done by cell cleavage,
each cell transferring its characteristics to its
daughter-cells. We may consequently here also
speak of phenomena of inheritance, and we shall
distinguish them as Asexual Inheritance. The
term Inheritance implies that the transferring of
characteristics takes place continually from genera-
tion to generation. But it is not necessary for the
characteristics to be apparent. Hybrids often do
not show their characteristics in an intermediate
form between the parental forms, but entirely
resemble in a certain respect one of their parents.
144

CHEMICAL HEREDITY

Mendel showed that in the second generation
the hidden characteristic of the other parent
becomes manifest in 25 per cent of the descendants.
So it must have been latent in the first generation.
Such cases of heredity we call Discontinuous
Heredity, continual manifestation of characteristics
Continuous Heredity.

Heredity is far from being an absolutely sharp
and marked conception. Phenomena of typical
sexual inheritance are connected by an innumer-
able range of intermediate stages with the pheno-
mena which we call typically transitory induc-
tions. One could even think that Inheritance
represents only the limit of longeval induction,
of which we cannot recognise the end, because the
duration of our time of observation is too short.
If we could follow up millions of generations, if we
could have the age of an eternal being, we might
find the phenomena of variation more striking
than the phenomena of inheritance. The best
materials with which it is possible to observe a
great number of generations in a few weeks are
microbes and bacteria. There is one case known
which illustrates the conception of inheritance
most instructively. The Bacillus prodigiosus is a
microbe which, under normal conditions, is very
noteworthy because of its production of a scarlet
colouring matter. When this bacterium is cul-
tivated at a temperature of 30 to 35 degrees it
gradually loses its colour. The interesting fact
L 145

CHEMICAL PHENOMENA IN LIFE

is now that the property of being colourless remains
when the microbe is again cultivated at the
ordinary temperature of 18 degrees. One would
feel inclined to suppose that it had lost its property
of producing the red pigment by the influence of
heat. The loss is undoubtedly hereditary, for
many generations are formed under normal
temperature conditions which are absolutely
without any red hue. But after a certain number
of generations, which may be many thousands, the
red hue returns, and the bacterium regains its
former appearance. Such phenomena seem to be
not very rare. If we were beings of quite short
duration of life, we would perhaps believe that the
loss of red pigment in these bacteria was real
inheritance. Since we can prove that after a great
number of generations the former property
returns, we call that Pseudo-Inheritance. But
we must bear in mind that there is no sharp
distinction between pseudo-inheritance and real
inheritance. The latter can only be considered
as a pseudo-inheritance which lasts for an infinitely
great number of generations. Chemical pheno-
mena in this territory will certainly be discovered,
and perhaps will contribute much towards making
these difficult questions clearer.

Phylogenetic investigations still contain many

more interesting chemical questions than we could

touch on in our short discussion. Well worth

consideration is the question whether the so-called

146

CHEMICAL HEREDITY

Biogenetical Law of Haeckel extends to chemical
phenomena. We know that the embryos of higher
animals show considerable morphological re-
semblances to lower animals, and so it is in plants.
The first stages of development in mosses resemble
algae, the first development of ferns reminds us
very strongly of liverworts. These facts are so
general that they have been summarised in the
rule : That the development of the individual
organism or the ontogeny represents a short re-
capitulation of the phytogeny. This law is hitherto
only based upon morphological facts. Since
morphological phenomena are always accom-
panied by chemical analogies, we may suppose
that the law of Biogenetics can be applied also to
chemical phenomena in life. Many reasons can
be produced to support this idea. The primitive
groups of higher plants, such as Mosses and Ferns,
and Gymnosperms, do not contain by far as
many different substances as the Phanerogams.
All the numerous glycosides, most alkaloids, and
the bitter principles occur in the phanerogamic
groups. The lowest plants of the classes Algae
and Fungi in general contain only the wide-
spread organic compounds, such as fats, carbo-
hydrates, or proteids. The Lichens, a highly
developed symbiotic group of Fungi, alone contain
a greater number of specific organic compounds
belonging to the class of benzene-derivatives.
The lowest Algae and Fungi as well as the Bacteria
147

CHEMICAL PHENOMENA IN LIFE

have essentially the chemical composition of
protoplasm. In Ontology we see that the young
tissues of higher plants do not yet contain the
different chemical compounds which are found in
the adult plants. Even here the chemical com-
position of the youngest cells is essentially that
of protoplasm.

148

INDEX

Adaptation, Chemical, 140
Adsorption, 49
Agglutination of Bacteria, 134
Agglutinins, 134
Aggressins, 134
Alcoholic Fermentation, 94
D'Alembert, 5
Alien Proteids, 132
Amicrons, 26
Amidases, 113
Anaerobiosis, 119
Anti-Enzymes, 99, 102
Antitoxins, 129
Armstrong, 115
Arrhenius, Sv., 107, 130, 131
Atavism, 139
Autocatalysis, 90
Autolysis, 14, 65

Bacteriolysins, 134
Baumann, 52
Berzelius, 85, 86, 97
Bimolecular Reactions, 80
Biochemistry, 5
Biogenetical Law, 147
Biology, Comparative, 3
— Experimental, 4
Blackman, F. Fr., 69, 105
Bredig, 24, 30, 89
Briicke, 11

Buchner, E., 66, 94, 118
Biitschli, 60

Cagniard Latour, 91
Carbohydrases, 113

L 2

Carboxylases, 113
Catalysis, 84
Catalytic Power, 85

— Reactions, 87
Catalysers, 86
Cataphoresis, 28
Cavendish, 5
Cell Turgor, 56

Chemical Reactions in Living

Matter, 62
Chemoses, 141
Chlorophyll, 59
Chloroplasts, 58
Coagulases, 113
Cohn, Ferd., 12
Colloidal Properties, 20
Colloids, 20

— Molecular Weight, 22

— Physical Properties, 22
Contact Effects, 85
Crystalloid Stage, 20
Cytoplasm, 13, 54
Cytotoxins, 128

Diastase, 85, 92
Diosmosis, 45
Dumas, 8

Ehrlich, 130, 131

Elective Assimilation of Soil

Constituents, 52
Emmerling, O., 116
Emulsin, 115
Emulsions, 27
Emulsion-Colloids, 30

149

INDEX

Endo-Enzymes, 96
Engine-Theories of Life, 14
Enzymes, 19, 91, 94

— Influence of Temperature
on, 103

— Intracellular, 96

— Syntheses by, 114
Enzyme Reactions, Optimum

of, 105

Esterases, 113
Etard, 18

Faraday, 21, 73
Fermentation, 91, 93
Ferments, 91

— Soluble, 93
Fisher, Em., 9

Foam - Structure of Proto-
plasm, 60, 71

Gels, 21, 48

Gibbs, W.,4i, 43

Goethe, 6

Graham, Th., 20, 21, 22, 32,

48
Gully, 52

Haeckel, 147

Hales, St., 4

Hardy, 30

Heredity, Continuous, 145

— Discontinuous, 145
Hill, A. Cr., 115
Van't Hoff, 68, 106, 115
Van 't Hoff's Rule, 69, 103
Hofmeister, Fr., 48, 50
Hormones, 127

Hudson, 109
Humic Acids, 52
Hyaloplasm, 34
Hydrolases, 113

Hydrolysis, 112
Hydrolytic Enzymes, 113

Immunochemistry, 129
Ingenhousz, 5
Inheritance, Chemical, 143

— Asexual, 144
Internal Secretion, 127
Ionic Reactions, 73
Ions, 21, 73

— Complex, 74
Isosmotic Solutions, 57

Kanitz, 69
Kelvin, 124
Kinases, 101
Kirchhoff, K., 85
Kuhne, II, 93
Kutzing, 92

La Mettrie, 5

Lavoisier, 5,110

Law of Nature, 2

Life, Engine-Theories of, 14

— Force, 7

— Process of, 6

— Stuff-Theories of, 15
Linder, 23

Lipases, 113
Loew, Osc., 1 6
Lyophil Colloids, 47
Lyophobic Colloids, 47

Macfadyan and Rowland, 66
Materialism, 5, 6
Matthaei, Miss, 69
Maupertuis, 5
Medium of Dispersion, 29
Mendel's Law, 139
Metabolism, 62
Metal Sols, 24
Microbic Ferments, 93

150

INDEX

Microns, 26
Microsomes, 13
Mitscherlich, 85
Mohl, H. v., ii
Monomolecular Reactions, 79
Morphoses, 141
Mutations, 137, 138

Nernst, 45
Newton, 5
Nucleus of the Cell, 54

Opsonins, 134
Organ-Proteids, 18
Organic Chemistry, 7

— Substances, 7

— Syntheses, 8
Osmosis, 20

— Theory of, 45
Osmotic Pressure, 32
Ostwald, 86

Overton, E., 38, 41, 42, 44
Oxidases, 113

Palladin, 66, 119

Pasteur, 92, 119

Payen and Persoz, 85, 92

Pfeffer, 32, 34, 87

Physiology, 4

Picton, 23

Plasmatic Membrane, 46

Plasmodium, Chemical Analy-
sis of, 15

Plasmolysis, 36

Plastids, 59

Plastine, 18

Poisonous Effects, 126

Poisons for Catalytic Effects,
90

Polioplasm, 34, 54, 55

Precipitin Reactions, 131

Priestley, 5

Primordial Utricle, n
Pro-Enzymes, 101
Proteases, 113
Protoplasm, n

— Chemical Analysis, 15

— Structure, 12

— Structure Theory of, 16
Protoplasmatic Membrane,

Protoplasmids, 18
Pseudo-Inheritance, 146

Quetelet, 137, 138
Quincke, 39, 44

Reactions of the First Order,

79

— Reversibility of, 8 1

— of the Second Order, 80
Reaction Velocity in Living

Matter, 72, 76
Reductases, 113, 121
R, G, T— Rule, 69
Reinke, 15, 18

— and Rodewald, 15
Release Actions, 87
Richardson's Law, 42
Rodewald, 15

Root, Excretions of the, 51

Salkowski, 65
Sarcode, 12
Saussure, 8, 116
Scheele, 5

Schoenbein, 93, 118
Schiitz, 107, 108
Schutz's Rule, 107
Schwann, Th., 91, 92
Secretion-Enzymes, 96
Semi-colloids, 23
Side Chain-Theory, 130
Sols, 21, 48

INDEX

Stuff-Theories of Life, 15

Submicrons, 26

O'Sullivan and Thompson,
1 08

Surface Tension of Proto-
plasm, 41, 43

Suspension-Colloids, 29

Suspensions, 27

Temperature, Influence on

Chemical Reactions, 67
Time Factor, 136
Traube, 41, 42
Tyndall's Phenomenon, 24

Uhlenhuth, 132
Ultramicroscope, 24

Variation, Chemical, 137
— Fluctuating, 137
Velocity of Reactions, 72
Vries, H. de, 36, 56, 57, 137,
138

Wohler, 8

Zsigmondy, 25
Zymase, 113
Zymogens, 101

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