Produced by David Garcia, James Nugen, Keith Edkins and
the Online Distributed Proofreading Team at
http://www.pgdp.net
Transcriber's note: A few typographical errors have been corrected: they
are listed at the end of the text.
* * * * *
THE MECHANISM OF LIFE
[Illustration: Osmotic Productions. [_Frontispiece_]
THE
MECHANISM OF LIFE
BY
DR. STEPHANE LEDUC
PROFESSEUR A L'ECOLE DE MEDECINE DE NANTES
TRANSLATED BY
W. DEANE BUTCHER
FORMERLY PRESIDENT OF THE ROENTGEN SOCIETY, AND OF THE
ELECTRO-THERAPEUTICAL SECTION OF THE ROYAL SOCIETY OF MEDICINE
"La nature a forme, et forme tous
les jours les etres les plus simples par
generation spontanee." LAMARCK.
[Illustration]
NEW YORK
REBMAN COMPANY
HERALD SQUARE BUILDING
141-145, WEST 36TH STREET
_First Impression March 1911_
_Second Impression January 1914_
_Printed in England_
* * * * *
{vii}
TRANSLATOR'S PREFACE
Professor Leduc's _Theorie Physico-chimique de la Vie et Generations
Spontanees_ has excited a good deal of attention, and not a little
opposition, on the Continent. As recently as 1907 the Academie des Sciences
excluded from its _Comptes Rendus_ the report of these experimental
researches on diffusion and osmosis, because it touched too closely on the
burning question of spontaneous generation.
As the author points out, Lamarck's early evolutionary hypothesis was
killed by opposition and neglect, and had to be reborn in England before it
obtained universal acceptance as the Darwinian Theory. Not unnaturally,
therefore, he turns for an appreciation of his work to the free air and
wide horizon of the English-speaking countries.
He has entitled his book "The Mechanism of Life," since however little we
may know of the origin of life, we may yet hope to get a glimpse of the
machinery, and perhaps even hear the whirr of the wheels in Nature's
workshop. The subject is of entrancing interest to the biologist and the
physician, quite apart from its bearing on the question of spontaneous
generation. Whatever view may be entertained by the different schools of
thought as to the nature and significance of life, all alike will welcome
this new and important contribution to our knowledge of the mechanism by
which Nature constructs the bewildering variety of her forms.
There is, I think, no more wonderful and illuminating spectacle than that
of an osmotic growth,--a crude lump of brute inanimate matter germinating
before our very eyes, putting forth bud and stem and root and branch and
leaf and fruit, with no stimulus from germ or seed, without even {viii} the
presence of organic matter. For these mineral growths are not mere
crystallizations as many suppose; they increase by intussusception and not
by accretion. They exhibit the phenomena of circulation and respiration,
and a crude sort of reproduction by budding; they have a period of vigorous
youthful growth, of old age, of death and of decay. They imitate the forms,
the colour, the texture, and even the microscopical structure of organic
growth so closely as to deceive the very elect. When we find, moreover,
that the processes of nutrition are carried on in these osmotic productions
just as in living beings, that an injury to an osmotic growth is repaired
by the coagulation of its internal sap, and that it is able to perform
periodic movements just as an animal or a plant, we are at a loss to define
any line of separation between these mineral forms and those of organic
life.
In the present volume the author has collected all the data necessary for a
complete survey of the mechanism of life, which consists essentially of
those phenomena which are exhibited at the contact of solutions of
different degrees of concentration. Whatever may be the verdict as to the
author's case for spontaneous generation, all will agree that the book is a
most brilliant and stimulating study, founded on the personal investigation
of a born experimenter.
The present volume is a translation of Dr. Leduc's French edition, but it
is more than this, the work has been translated, revised and corrected, and
in many places re-written, by the author's own hand. I am responsible only
for the English form of the treatise, and can but regret that I have been
able to reproduce so imperfectly the charm of the original.
W. DEANE BUTCHER.
EALING.
* * * * *
{ix}
PREFACE TO THE ENGLISH EDITION
C'est par l'initiative du Dr. Deane Butcher que cette ouvrage est presente
aux lecteurs anglais, a la race qui a dote l'humanite de tant de
decouvertes originales, geniales et d'une portee tres generale.
Comme un etre vivant, une idee exige pour naitre et se developper le germe
et le milieu de developpement. Il est indeniable que le peuple
anglo-americain constitue un milieu particulierement favorable a la
naissance et au developpement des idees nouvelles.
Pendant notre collaboration le Dr. Deane Butcher a ete un critique
judicieux et eclaire, tous les changements dans l'edition anglaise sont dus
a ses observations. Il s'est assimile l'ouvrage pour le traduire, et dans
beaucoup de parties, il a mis plus de clarte et de concision qu'il n'y en
avait dans le texte original.
STEPHANE LEDUC.
NANTES, 1911.
* * * * *
{xi}
TABLE OF CONTENTS
PAGE
TRANSLATOR'S PREFACE vii
AUTHOR'S PREFACE ix
INTRODUCTION xiii
I. LIFE AND LIVING BEINGS 1
II. SOLUTIONS 14
III. ELECTROLYTIC SOLUTIONS 24
IV. COLLOIDS 36
V. DIFFUSION AND OSMOSIS 43
VI. PERIODICITY 67
VII. COHESION AND CRYSTALLIZATION 78
VIII. KARYOKINESIS 89
IX. ENERGETICS 97
X. SYNTHETIC BIOLOGY 113
XI. OSMOTIC GROWTH: A STUDY IN MORPHOGENESIS 123
XII. THE PHENOMENA OF LIFE AND OSMOTIC PRODUCTIONS:
A STUDY IN PHYSIOGENESIS 147
XIII. EVOLUTION AND SPONTANEOUS GENERATION 160
* * * * *
{xiii}
INTRODUCTION
Life was formerly regarded as a phenomenon entirely separated from the
other phenomena of Nature, and even up to the present time Science has
proved wholly unable to give a definition of Life; evolution, nutrition,
sensibility, growth, organization, none of these, not even the faculty of
reproduction, is the exclusive appanage of life.
Living things are made of the same chemical elements as minerals; a living
being is the arena of the same physical forces as those which affect the
inorganic world.
Life is difficult to define because it differs from one living being to
another; the life of a man is not that of a polyp or of a plant, and if we
find it impossible to discover the line which separates life from the other
phenomena of Nature, it is in fact because no such line of demarcation
exists--the passage from animate to inanimate is gradual and insensible.
The step between a stalagmite and a polyp is less than that between a polyp
and a man, and even the trained biologist is often at a loss to determine
whether a given borderland form is the result of life, or of the inanimate
forces of the mineral world.
A living being is a transformer of matter and energy--both matter and
energy being uncreateable and indestructible, i.e. invariable in quantity.
A living being is only a current of matter and of energy, both of which
change from moment to moment while passing through the organism.
That which constitutes a living being is its form; for a living thing is
born, develops, and dies with the form and structure of its organism. This
ephemeral nature of the living being, which perishes with the destruction
of its form, is in {xiv} marked contrast to the perennial character of the
matter and the energy which circulate within it.
The elementary phenomenon of life is the contact between an alimentary
liquid and a cell. For the essential phenomenon of life is nutrition, and
in order to be assimilated all the elements of an organism must be brought
into a state of solution. Hence the study of life may be best begun by the
study of those physico-chemical phenomena which result from the contact of
two different liquids. Biology is thus but a branch of the
physico-chemistry of liquids; it includes the study of electrolytic and
colloidal solutions, and of the molecular forces brought into play by
solution, osmosis, diffusion, cohesion, and crystallization.
In this volume I have endeavoured to give as much of the science of
energetics as can be treated without the use of mathematical formulae; the
conception of entropy and Carnot's law of thermodynamics are also
discussed.
The phenomena of catalysis and of diastatic fermentation have for the first
time been brought under the general laws of energetics. This I have done by
showing that catalysis is only one instance of the general law of the
transformation of potential into kinetic energy, viz. by the intervention
of a foreign exciting and stimulating energy which may be infinitely
smaller than the energy it transforms. This conception brings life into
line with other catalytic actions, and shows us a living being as a store
of potential energy, to be set free by an external stimulus which may also
excite sensation.
In a subsequent chapter I have dealt with the rise of Synthetic Biology,
whose history and methods I have described. It is only of late that the
progress of physico-chemical science has enabled us to enter into this
field of research, the final one in the evolution of biological science.
The present work contains some of the earliest results of this synthetic
biology. We shall see how it is possible by the mere diffusion of liquids
to obtain forms which imitate with the greatest accuracy not only the
ordinary cellular tissues, but the more complicated striated structures,
such as muscle and mother-of-pearl. We shall also see how it is {xv}
possible by simple liquid diffusion to reproduce in ordered and regular
succession complicated movements like those observed in the karyokinesis of
the living cell.
The essential character of the living being is its Form. This is the only
characteristic which it retains during the whole of its existence, with
which it is born, which causes its development, and disappears with its
death. The task of synthetic biology is the recognition of those
physico-chemical forces and conditions which can produce forms and
structures analogous to those of living beings. This is the subject of the
chapter on Morphogenesis.
The last chapter deals with the doctrine of Evolution. The chain of life is
of necessity a continuous one, from the mineral at one end to the most
complicated organism at the other. We cannot allow that it is broken at any
point, or that there is a link missing between animate and inanimate
nature. Hence the theory of evolution necessarily admits the
physico-chemical nature of life and the fact of spontaneous generation.
Only thus can the evolutionary theory become a rational one, a stimulating
and fertile inspirer of research. We seek for the physico-chemical forces
which produce forms and structures analogous to those of living beings, and
phenomena analogous to those of life. We study the alterations in
environment which modify these forms, and we seek in the past history of
our planet for those natural phenomena which have brought these
physico-chemical forces into play. In this way we may find the road which
will, we hope, lead some day to the discovery of the origin and the
evolution of life upon the earth.
* * * * *
{1}
THE MECHANISM OF LIFE
CHAPTER I
LIFE AND LIVING BEINGS
Primitive man distinguished but two kinds of bodies in nature, those which
were motionless and those which were animated. Movement was for him the
expression of life. The stream, the wind, the waves, all were alive, and
each was endowed with all the attributes of life--will, sentiment, and
passion. Ancient Greek mythology is but the poetic expression of this
primitive conception.
In the evolution of the intelligence, as in that of the body, the
development of the individual is but a repetition of the development of the
race. Even now children attribute life to everything that moves. For them a
little bird still lives in the inside of a watch, and produces the
tick-tick of the wheels. In modern times, however, we have learnt that
everything in nature moves, so that motion of itself cannot be considered
as the characteristic of life.
Heraclitus aptly compares life to a flame. Aristotle says, "Life is
nutrition, growth, and decay,--having for its cause a principle which has
its end in itself, namely [Greek: entelecheia]." This principle is itself
in need of definition, and Aristotle only substitutes one unknown epithet
for another.
Bichat defined life as the ensemble of the functions which resist death.
This is to define life in terms of death,--but death is but the end of
life, and cannot be defined without first defining life. Claude Bernard
rejects all definition of life as insufficient, and incompatible with
experimental science. {2}
Some modern physiologists regard sensibility, others irritability, as the
characteristic of life, and define life as the faculty of responding, by
some sort of change, to an external stimulus. As in the case of movement,
we have found by more attentive observation that this faculty also is
universal in nature. There is no action without reaction; an elastic body
repels the body that strikes it. Every object in nature dilates with heat,
contracts with cold, and is modified by the light which it absorbs.
Everything in nature responds to exterior action by a change, and hence
this faculty cannot be the characteristic of life.
A distinguished professor of physiology was accustomed to teach that the
disproportion between action and reaction was the characteristic of life.
"Allow a gramme weight to fall on a nerve, and the muscle will raise a
weight of ten grammes. This disproportion is the characteristic of life."
But there is a much greater disproportion between action and reaction when
the friction of a match blows up a powder factory, or the turning of a
switch lights the lamps and animates the tramways and the motors of a great
city. The disproportion between action and reaction is therefore no
characteristic of life.
The essential characteristic of life is often said to be nutrition--the
phenomenon by which a living organism absorbs matter from its environment,
subjects it to chemical metamorphosis, assimilates it, and finally ejects
the destructive products of metamorphosis into the surrounding medium. But
this characteristic is also common to a great number of ordinary chemical
reactions, so that we cannot call it peculiar to life. Consider, for
instance, a fragment of calcium chloride immersed in a solution of sodium
carbonate. It absorbs the carbonic ion, incorporates it into a molecule of
calcium carbonate, and ejects the chlorine ion into the surrounding medium.
It may be argued that this is merely a chemical process, since the
substance which determines the reaction is also modified, the chloride of
calcium changing into carbonate of calcium. But every living thing is also
changing its chemical {3} constitution during every moment of its
existence,--it is this change which constitutes the process of senile
involution. The substance of the child is other than that of the ovum, and
the substance of the adult is not that of the child. Hence we cannot regard
nutrition as the exclusive characteristic of life.
Other authorities regard growth and organization as the essentials of life.
But crystals also grow. It was said that the growth of a crystal differed
from that of a living thing, in that the former grew by the addition of
material from without--the juxtaposition of bricks, as it were--while the
latter grew by intussusception, an introduction of fresh material into the
substance of the organism. A crystal, moreover, was homogeneous, while the
tissues of a living being were differentiated--such differentiation
constituting the organization. At the present time, however, we recognize
the existence of a great variety of purely physical productions, the
so-called "osmotic growths," which increase by a process of
intussusception, and develop therefrom a marvellous complexity of
organization and of form. Hence growth and organization cannot be
considered as the essential characteristics of life.
Since, then, we are totally unable to define the exact boundary which
separates life from the physical phenomena of nature, we may fairly
conclude that no such separation exists. This is in conformity with the
"law of continuity,"--the principle which asserts that all the phenomena of
nature are continuous in time and space. Classes, divisions, and
separations are all artificial, made not by nature but by man. All the
forms and phenomena of nature are united by insensible transition; it is
impossible to separate them, and in the distinction between living and
non-living things we must content ourselves with relative definitions,
which are far from being precise.
Life can only be defined as the sum of all phenomena exhibited by living
beings, and its definition thus becomes a mere corollary to the definition
of a living being.
The true definition of a living being is that it is a transformer of
energy, receiving from its environment the energy {4} which it returns to
that environment under another form. All living organisms are transformers
of energy.
A living organism is also a transformer of matter. It absorbs matter from
its environment, transforms it, and returns it to its environment in a
different chemical condition. Living things are chemical transformers of
matter.
Living beings are also transformers of form. They commence as a very simple
form, which gradually develops and becomes more complicated.
The matter of which a living organism is constituted consists essentially
of certain solutions of crystalloids and colloids. To this we may add an
osmotic membrane to contain the liquids, and a solid skeleton to support
and protect them. Finally, it would seem that a colloid of one of the
albuminoid groups is a necessary constituent of every living being.
We may say, then, that a living being is a transformer of energy and of
matter, containing certain albuminoid substances, with an evolutionary
form, the constitution of which is essentially liquid.
A living being has but a limited duration. It is born, develops, becomes
organized, declines and dies. Through all the metamorphoses of form, of
substance, and of energy, informing the whole course of its existence,
there is a certain co-ordination, a certain harmony, which is necessary for
the conservation of the individual. This harmony we call Life. Discord is
disease,--the total cessation of the harmony is Death. When the form is
profoundly altered and the substance changed, the transformation of energy
no longer follows its regular course, the organism is dead.
After death the colloids which have constituted the form of the living
thing pass from their liquid state as "sols" into their coagulated state as
"gels." The metamorphoses of form, substance, and energy still continue,
but no longer harmoniously for the conservation of the individual, but in
dis-harmony for its dissolution. Finally, the form of the individual
disappears, the substance and the energy of the living being is resolved
and dispersed into other bodies and other phenomena. {5}
The results hitherto obtained from the study of life seem but
inconsiderable when compared with the time and labour devoted to the
question. Max Verworn exclaims, "Are we on a false track? Do we ask our
questions of Nature amiss, or do we not read her answers aright?"
Each branch of science at its commencement employs only the simpler methods
of observation. It is purely descriptive. The next step is to separate the
different parts of the object studied--to dissect and to analyse. The
science has now become analytical. The final stage is to reproduce the
substances, the forms, and the phenomena which have been the subject of
investigation. The science has at last become synthetical.
Up to the present time, biology has made use only of the first two methods,
the descriptive and the analytical. The analytical method is at a grave
disadvantage in all biological investigations, since it is impossible to
separate and analyse the elementary phenomena of life. The function of an
organ ceases when it is isolated from the organism of which it forms a
part. This is the chief cause of our lack of progress in the analysis of
life.
It is only recently that we have been able to apply the synthetic method to
the study of the phenomena of life. Now that we know that a living organism
is but the arena for the transformation of energy, we may hope to reproduce
the elementary phenomena of life, by calling into play a similar
transformation of energy in a suitable medium.
Organic chemistry has already obtained numerous victories in the same
direction, and the rapid advance in the production of organic bodies by
chemical synthesis may be considered the first-fruits of synthetic biology.
A phenomenon is determined by a number of circumstances which we call its
causes, and of which it is the result. Every phenomenon, moreover,
contributes to the production of other phenomena which are called its
consequences. In order therefore to understand any phenomenon in its
entirety, we must determine all its causes both qualitatively and
quantitatively.
Phenomena succeed one another in time as consequences {6} one of another,
and thus form an uninterrupted chain from the infinite of the past into the
infinite of the future. A living being gathers from its entourage a supply
of matter and of energy, which it transforms and returns. It is part and
parcel of the medium in which it lives, which acts upon it, and upon which
it acts. The living being and the medium in which it exists are mutually
interdependent. This medium is in its turn dependent on its entourage,--and
so on from medium to medium throughout the regions of infinite space.
One of the great laws of the universe is the law of continuity in time and
space. We must not lose sight of this law when we attempt to follow the
metamorphoses of matter, of energy and of form in living beings. Evolution
is but the expression of this law of continuity, this succession of
phenomena following one another like the links of a chain, without
discontinuity through the vast extent of time and space.
The other great universal law, that of conservation, applies with equal
force to living and to inanimate things. This law asserts the
uncreateability and the indestructibility of matter and of energy. A given
quantity of matter and of energy remains absolutely invariable through all
the transformations through which it may pass.
We need not here discuss the question of the possible transformation of
matter into ether, or of ether into ponderable matter. Such a
transformation, if it exists, would have but little bearing on the
phenomena of life. Moreover, it also will probably be found to conform to
the law of conservation of energy.
In marked contrast to the permanence of matter and of energy is the
ephemeral nature of form, as exhibited by living beings. Function, since it
is but the resultant of form, is also ephemeral. All the faculties of life
are bound up with its form,--a living being is born, exists, and dies with
its form.
The phenomena of life may in certain cases slow down from their normal
rapidity and intensity, as in hibernating {7} animals, or be entirely
suspended, as in seeds. This state of suspension of life, of latent life as
it were, reminds us of a machine that has been stopped, but which retains
its form and substance unaltered, and may be started again whenever the
obstacle to its progress is removed.
During the whole course of its life a living being is intimately dependent
on its entourage. For example, the phenomena of life are circumscribed
within very narrow limits of temperature. A living organism, consisting as
it does essentially of liquid solutions, can only exist at temperatures at
which such solutions remain liquid, i.e. between 0deg C. and 100deg C.
Certain organisms, it is true, may be frozen, but their life remains in a
state of suspension so long as their substance remains solid. Since the
albuminoid substances which are a necessary component of the living
organism become coagulated at 44deg C., the manifestations of life diminish
rapidly above this temperature. The intensity of life may be said to
augment gradually as the temperature rises from 0deg to 40deg, and then to
diminish rapidly as the temperature rises above that point, becoming nearly
extinct at 60deg C.
Another condition indispensable to life is the presence of oxygen. Life,
compared by Heraclitus to a flame, is a combustion, an oxydation, for which
the presence of oxygen at a certain pressure is indispensable. There are,
it is true, certain anaerobic micro-organisms which apparently exist
without oxygen, but these in reality obtain their oxygen from the medium in
which they grow.
Life is also influenced by light, by mechanical pressure, by the chemical
composition of its entourage, and by other conditions which we do not as
yet understand. In each case the conditions which are favourable or noxious
vary with the nature of the organism, some living in air, some in fresh
water, and others in the sea.
Formerly it was supposed that the substance of a living being was
essentially different from that of the mineral world, so much so that two
distinct chemistries were in existence--organic chemistry, the study of
substances derived from bodies which had once possessed life, and inorganic
chemistry, dealing {8} with minerals, metalloids, and metals. We now know
that a living organism is composed of exactly the same elements as those
which constitute the mineral world. These are carbon, oxygen, hydrogen,
nitrogen, phosphorus, calcium, iron, sulphur, chlorine, sodium, potassium,
and one or two other elements in smaller quantity. It was formerly supposed
that the organic combinations of these elements were found only in living
organisms and could be fashioned only by vital forces. In more recent
times, however, an ever increasing number of organic substances have been
produced in the laboratory.
Organic bodies may be divided into four principal groups. (1)
_Carbohydrates_, including the sugars and the starches, all of which may be
considered as formed of carbon and water. (2) _Fats_, which may be
considered chemically as the ethers of glycerine, combinations of one
molecule of glycerine and three molecules of a fatty acid, with elimination
of water. (3) _Albuminoids_, substances whose molecules are complex,
containing nitrogen and sulphur in addition to carbon, oxygen, and
hydrogen. The albuminoid of the cell nucleus also contains phosphorus, and
the haemoglobin of the blood contains iron. (4) _Minerals_ or inorganic
elements, such as chloride of sodium, phosphate of calcium, and carbonic
acid. This group also includes water, which is the most important
constituent, since it forms more than a moiety of the substance of all
living creatures.
Woehler in 1828 accomplished the first synthesis of an organic substance,
urea, one of the products of the decomposition of albumin. Since then a
large number of organic substances have been prepared by the synthesis of
their inorganic elements. The most recent advance in this direction is that
of Emile Fischer, who has produced polypeptides having the same reactions
as the peptones, by combining a number of molecules of the amides of the
fatty acids.
In the further synthesis of organic compounds the problems we have before
us are of the same order as those already solved. There is no essential
difference between organic and inorganic chemistry; living organisms are
formed of the {9} same elements as the mineral world, and the organic
combinations of these elements may be realized in our laboratories, just as
in the laboratory of the living organism.
Not only so, but a living being only borrows for a short time those mineral
elements which, after having passed through the living organism, are
returned once again to the mineral kingdom from which they came.
All matter has life in itself--or, at any rate, all matter susceptible of
incorporation in a living cell. This life is potential while the element is
in the mineral state, and actual while the element is passing through a
living organism.
Mineral matter is changed into organic matter in its passage through a
vegetable organism. The carbonic acid produced by combustion and
respiration is absorbed by the chlorophyll of the leaves under the stimulus
of light--the oxygen of the carbonic acid being returned to the air, while
the carbon is utilized by the plant for the formation of sugar, starch,
cellulose, and fats.
Thus plants are fed in great part by their leaves, taking an important part
of their nourishment from the air, while by their roots they draw from the
earth the water, the phosphates, the mineral salts, and the nitrates
required for the formation of their albuminoid constituents. A vegetable is
a laboratory in which is carried out the process of organic synthesis by
which mineral materials are changed into organic matter. The first
synthetic reaction is the formation of a molecule of formic aldehyde,
CH_2O, by the combination of a molecule of water with an atom of carbon.
From this formic aldehyde, or formol, we may obtain all the various
carbohydrates by simple polymerization, i.e. by the association of several
molecules, with or without elimination of water. Thus two molecules of
formol form one molecule of acetic acid, 2CH_2O = C_2H_4O_2. Three
molecules of formol form a molecule of lactic acid, 3CH_2O = C_3H_6O_3. Six
molecules of formol represent glucose and levulose, 6CH_2O = C_6H_{12}O_6.
Twelve molecules of formol minus one molecule of water form saccharose,
lactose, cane sugar, and sugar of milk, 12CH_2O = C_{12}H_{22}O_{11} +
H_2O; _n_ times six {10} molecules of formol minus one molecule of water,
_n_(C_6H_{10}O_5), form starch and cellulose.
Animals derive their nourishment from vegetables either directly, or
indirectly through the flesh of herbivorous animals. The mineral matter,
rendered organic in its passage through a vegetable growth, is finally
returned by the agency of animal organisms to the mineral world again, in
the form of carbonic acid, water, urea, and nitrates. Thus vegetables may
be regarded as synthetic agents, and animals and microbes as agents of
decomposition. Here also the difference is only relative, for in certain
cases vegetables produce carbonic acid, while some animal organisms effect
synthetic combinations. Moreover, there are intermediary forms, such as
fungi, which possessing no chlorophyll are nourished like animals by
organic matter, and yet like vegetables are able to manufacture organic
matter from mineral salts.
The work of combustion begun by the animal organism is finished by the
action of micro-organisms, who complete the oxydation--the
re-mineralization of the chemical substances drawn originally from the
inorganic world by the agency of plant life.
To sum up. Vegetables obtain their nourishment from mineral substances,
which they reduce, de-oxydize, and charge with solar energy. Animal
organisms on the contrary oxydize, and micro-organisms complete the
oxydation of these substances, returning them to the mineral world as
water, carbonates, nitrates, and sulphates.
Thus matter circulates eternally from the mineral to the vegetable, from
the vegetable to the animal world, and back again. The matter which forms
our structure, which is to-day part and parcel of ourselves, has formed the
structure of an infinite number of living beings, and will continue to
pursue its endless reincarnation after our decease.
This endless cycle of life is also an endless cycle of energy. The
combination of carbon with water carried out by the agency of chlorophyll
can only take place with absorption of energy. This energy comes directly
from the sun, the red and orange light radiations being absorbed by the
chlorophyll. {11} The arrest of vegetation during the winter months is due
not so much to the lowering of temperature as to the diminution of the
radiant energy received from the sun. In the same way shade is harmful to
vegetation, since the radiant energy required for growth is prevented from
reaching the plant.
The energy radiated by the sun is accumulated and stored in the plant
tissues. Later on, animals feed on the plants and utilize this energy,
excreting the products of decomposition, _i.e._ the constituents of their
food minus the energy contained in it. Thus the whole of the energy which
animates living beings, the whole of the energy which constitutes life,
comes from the sun. To the sun also we owe all artificial heat, the energy
stored up in wood and coal. We are all of us children of the sun.
The radiant energy of the sun is transformed by plants into chemical
energy. It is this chemical energy which feeds the vital activity of
animals, who return it to the external world under the form of heat,
mechanical work, and muscular contraction, light in the glow-worm,
electricity in the electric eel.
There is a marked difference between the forms affected by organic and
inorganic substances. The forms of the mineral world are those of
crystals--geometrical forms, bounded by straight lines, planes, and regular
angles. Living organisms, on the contrary, affect forms which are less
regular--curved surfaces and rounded angles. The physical reason for this
difference in form lies in a difference of consistency, crystals being
solid, whereas living organisms are liquids or semi-liquids. The liquids of
nature, streams and clouds and dewdrops, affect the same rounded forms as
those of living organisms.
Living beings for the most part present a remarkable degree of symmetry.
Some, like radiolarians and star-fish, have a stellate form. In plants the
various organs often radiate from an axis, in such a manner that on turning
the plant about this axis the various forms are superposed thrice, four, or
more often five times in one complete revolution. It is remarkable how
often this number five recurs in the {12} divisions and parts of a living
organism. In other cases the similar parts are disposed symmetrically on
either side of a median line or plane, giving a series of homologous parts
which are not superposable.
The most important characteristic of a living being is its form. This is
implicitly admitted by naturalists, who classify animals and plants in
genera and species according to the differences and analogies of their
form.
All living beings are composed of elementary organizations called cells. In
its complete state, a cell consists of a membrane or envelope containing a
mass of protoplasm, in the centre of which is a nucleus of differentiated
protoplasm. This nucleus may in its turn contain a nucleolus. In some cases
the cell is merely a protoplasmic mass without a visible envelope, so that
a cell may be defined as essentially a mass of protoplasm provided with a
nucleus.
A living organism may consist merely of a single cell, which is able alone
to accomplish all the functions of life. Most living beings, however,
consist of a collection of innumerable cells forming a cellular association
or community. When a number of cells are thus united to constitute a single
living being, the various functions of life are divided among different
cellular groups. Certain cells become specialized for the accomplishment of
a single function, and to each function corresponds a different form of
cell. It is thus easy to recognize by their form the nerve cells, the
muscle cells which perform the function of movement, and the glandular
cells which perform the function of secretion. The cells of a living being
are microscopic in size, and it is remarkable that they never attain to any
considerable dimensions.
In order that life may be maintained in a living organism, it is necessary
that a continual supply of aliment should be brought to it, and that
certain other substances, the waste-products of combustion, should be
eliminated. In order to be absorbed and assimilated, the alimentary
substances must be presented to the living organism in a liquid or gaseous
state. Thus the essential condition necessary for the {13} maintenance of
life is the contact of a living cell with a current of liquid. The
elementary physical phenomenon of life is the contact of two different
liquids. This is the necessary condition which renders possible the
chemical exchanges and the transformations of energy which constitute life.
It is in the study of the phenomena of liquid contact and diffusion that we
may best hope to pierce the secrets of life. The physics of vital action
are the physics of the phenomena which occur in liquids, and the study of
the physics of a liquid must be the preface and the basis of all inquiry
into the nature and origin of life.
* * * * *
{14}