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Pro Veritate"















THE word Biology, which seems to have been employed for
the first time by Treviranus, is far from bearing in the
scientific vocabulary a completely settled import. It may
not be unprofitable to determine the sense of the word.
Etymologically it signifies literally " science of life," and
embraces everything relating, intimately or remotely, to the
study of organised beings ; that is to say, a whole group of
sciences, among which is comprehended Anthropology, for
instance. It is in this encyclopaedical sense that Auguste
Comte took the word " Biology," though as far as we our-
selves are concerned we intend to give it a sense much more
restricted. Under the designation " Biology," we merely
place the exposition and the coordination of all the great
facts and great laws of life, or nearly what is usually under-
stood by " General Physiology," when this denomination is
applied to the two organic kingdoms. In this volume we
have simply attempted to state concisely what life is, and
how organised beings are nourished, grow, are reproduced,
move, feel and think.


Even while limiting ourselves to this comparatively re-
stricted domain, we have had to consider, to group, to con-
dense and to classify, an enormous mass of facts derived
from all the natural sciences. Among these facts, numerous
as the stars of the heaven and the sands of the sea, we
have been compelled to make a choice, and to select as much
as possible what was most important, most significative, most

We hope that the learned men who devote themselves to
special subjects may find in our modest production some new
combinations, perchance some of those general views which
are sometimes lacking to certain men in other respects very
distinguished, but who abide too closely in this or that district
of knowledge, as happens often in this age when the division
of scientific labour is carried to excess. Nevertheless, we do
not write for scientific men. We wish especially to be read
by the mass of enlightened people, whom our very incom-
plete system of public instruction has left almost unacquainted
with Biology. In effect, our best establishments for secondary
instruction limit their ambition to imparting sufficiently
complete ideas of physics, and very incomplete ideas con-
cerning chemistry ; but they stop too timidly on the threshold
of Biology, the mysteries of which are accessible? only to a
small number of special men. This is a defect exceedingly
deplorable, exceedingly prejudicial to general progress. It is
on account of this defect that so many false and even
pernicious ideas continue to find acceptance and empire in
public opinion ; hence it is, in a great measure, that true
philosophy, or rather that philosophy which is alone solid
and sound, that which flows directly and legitimately from


observation and experiment, has such difficulty in diffusing

The object of our little book is to remedy this serious
educational deficiency in those who are otherwise enlightened.
It is therefore a work of vulgarisation. Certain scientific
men, too strictly confined within their own circle, and whose
horizon is bounded by the walls of their laboratories, pro-
nounce, with disdain, though unjustly, this term vulgar-
isation. To find the truth is surely a noble labour ; but what
is the value of the discovered truth, if care is not taken to
propagate it, to introduce it into the patrimony of general
knowledge ?

On the other hand, it must be granted that the work of
popularising has been brought somewhat into disrepute by a
crowd of pseudo-scientific publications, the authors of 'which,
trusting too little to the intelligence of the reader, either
administer only an infinitesimal dose of science, or think
themselves obliged to dilute the main idea with a deluge of
light or pleasing words, sacrificing thus at once to the most
amiable and most dangerous of our national peculiarities.
Science only deserves its name upon condition of preserving
a somewhat austere nobleness. For our part we have taken
care not to rob science of that which constitutes its strength,
and for this we trust the reader will give us credit. In our
opinion there is not a person of moderate intelligence who
will not be able, at the cost of a slight mental effort, to read
and comprehend this book ; and we think also that by such
a perusal of it, sufficiently clear and complete ideas of Biology
will have been imparted.

This is not a polemical work, but rather an exposition


of facts. Nevertheless, amongst these facts are some which
are indisputable ; also, when we have met with them, we
have not hesitated to formulate the conclusions or induc-
tions which resulted from them. We have always done this
temperately and with brevity, and without having any other
motive than the love of truth.

We trust that this volume may be read, and that
profitably, and that it may awaken, in a large number
of its readers, love of and respect for science, namely, that
which alone, in these sad times, is at once a refuge and
a hope.











THE sciences of observation demand at the outset from him who
wishes to cultivate them an act of faith^ Though it is per-
fectly incontestable that the exterior world manifests itself to
us solely by exciting in our mind an incessant series of phe-
nomena of consciousness, of phenomena called subjective, we are
nevertheless compelled, unless we wish to plunge into the doubt
applauded by Pyrrho and Berkeley, to believe our senses as
honest and sincere witnesses when they signalise to us the exist-
ence, apart from our own being, of a vast material universe, the
elements whereof, without pause in movement, awaken in us, by
acting on our organism, impressions, sensations, and consequently
ideas and desires.

The exterior world exists independently of our conscious life ;
it was when as yet we were not ; and it will be when we are no

2 BIOLOGY. [Boos i.

more. Without stopping, as a few years ago M. Littre did, to
discuss the point whether the certitude of the existence of the
external world is of first or second quality, leaving aside every
metaphysical refinement, we must first firmly believe in the real
existence of the external world ; because all our senses cease not
to cry to us in every tone that the objective, the Non-He of the psy-
chologists, is not a chimera, because the contrary opinion would
strike with nullity all observation, all experience, all reasoning,
all knowledge.

The reality of the exterior world once admitted, and man
never having been led to doubt that reality, except through a
species of intellectual depravation, people naturally inquired
what could be the internal constitution of the substance of the
universe. They suspected that behind the appearance infinitely
mobile and varied of the exterior phenomena there might exist
a general and related force. Our object in this work not being
to pass in review the opinions or the reveries of the different
philosophical schools, we make haste to expound the most pro-
bable theories and systems, those which observation has confirmed,
and which by slow degrees have conquered in science their right
of citizenship.

Leucippus seems to have been the first to have had the intuition
of the most rational theory on the constitution of the universal
substance. In his opinion this substance is a discontinuous mass
of granules, solid, infinitely small, separated by void spaces. It
is " the void mingled with solid," according to an expression of

Democritus admitted that these primordial granules were full,
impenetrable, moreover insecable, and, for this last reason, he
called them atoms? But the conception of atoms, full and dis-

1 For what is it that Democritus says? "That there are substances in
infinite number, which are called atoms, because they cannot be divided, which
are, however, different, which have no quality whatever, are impassible, which
are dispersed here and there in the infinite void, which approach each other,
gather themselves together, enter into conjunction ; that from these assem-
blages one result appears as water, another as fire, another as tree, another


persed through the limitless void of the universe, did not furnish
a sufficiently precise account of the constitution of bodies.
Epicurus appeared, whose doctrine was so magnificently sung
by the great poet Lucretius. lie immensely improved the
atomic theory of Leucippus and Democritus by vivifying atoms,
and by supposing them endowed with spontaneous movement.
From the mobility of atoms resulted their various aggregations
and the dissemblances of bodies. According to Epicurus, atoms
of necessity mingled together, intertwined, literally caught and
clung to each other. A philosopher who had the talent to
preach and to propagate in France the atomic theoiy without
seeming to offend the orthodoxy of his epoch, which was still
very suspicious, Gassendi, restored to honour the atomic doctrine
of the ancients. He admits, according to the expression of
Epicurus, that "that which is moves in that which is not,"
that is, that atoms are not in contact, but that they are
separated by void spaces.

Thus then, according to this theory, the world is composed
of an innumerable quantity of atoms, mobile, infinitely small,
distant from each other. These atoms are in a perpetual state
of movement, rushing toward each other, repelling each other,
for they have their sympathies and antipathies. It is from
the diversity of their affinities that result their exceedingly
diversified modes of grouping and the variety of the external
world. It is by their vibrations, their oscillations that they
reveal themselves to man by impressing his organs of sense.
They have as essential qualities inalterability, eternity. When
they gather together, new bodies are formed ; when they dis-
aggregate, bodies previously existing dissolve and seem to vanish.
They are unhewn stones which have passed, pass, and are

as man ; that everything consists of atoms, which he also calls ideas, and that
nothing else exists, forasmuch as generation cannot arise from that which is
not while likewise what 'exists cannot cease to be, because atoms are so firm
that they cannot change nor alter nor suffer." PLUTARCH, Miscellaneous
Works : Against the Epicurean Colotcs; Amyot's translation, Clavier's
edition, vol. xx., Paris, 1803.

B 2


destined evermore to pass from one edifice to another. Their
totality constitutes the general substance of the universe, and,
in reality, this general substance undergoes no other changes
than modifications in the distribution of its constituent ele-
ments. All the phenomena, all the varied aspects, all the
revolutions of the universe can be referred essentially to simple
atomic displacements.

This grand theory, so admirably simple and seductive, would
be nothing but a brilliant speculation, if facts, numerous and
rigorously observed, did not now serve it as basis and demon-

We rapidly enumerate the most important of these facts, which
belong for the most part to the domain of Physics and Chemistry.
Wenzel, Bichter, Proust proved first of all that in chemical
compositions and decompositions, bodies combine according to
proportions rigorously defined. Dalton formulated the law of
multiple proportions, and deduced therefrom naturally that
matter is constituted by atoms extended, having a constant
weight, and that those atoms are of various species.

When atoms of the same species come into juxtaposition, we
have what we call simple bodies, such as hydrogen, oxygen,
azote. On the contrary, the bodies called compound result from
the juxtaposition of atoms of diversified nature, whence come
acids, salts, oxides, and also all the unstable and complex
compounds which constitute organic substances.

This is not all : to the law of Dalton the law of Avogadro
and of Ampere is adjoined. This last law establishes that all
gases, temperature and pressure being equal, have the same
elastic force. But as this force is probably due to the shock
of atoms or groups of atoms, molecules, on the sides of the
vessels which imprison the gases, we must admit that in the
conditions aforesaid all gases contain, under the same volume,
the same number of molecules or of atoms.

Finally, Dulong and Petit have been able to show, experi-
mentally, that the atoms of simple bodies all possess the same
specific heat.


All these great laws, slowly evolved by observation and ex-
periment, have transformed into a solid scientific theory the
brilliant but vague intuition of the thinkers of ancient Greece.
With ground so firm to rest on, chemistry has been able to
particularise more, to study in some sort the individual cha-
racter of atoms ; in scientific language, it has arrived at the
notion of atomicity.

Atoms have as general characteristics extension, impenetra-
bility, indestructibility, and eternal activity. But these general
characteristics exclude not a number of specific differences.
The progress of chemistry will no doubt show us what amount
of truth there is in the hypotheses of Dumas and of Lockyer,
according to which the simple bodies of chemistry as it now
exists are merely indecomposed bodies. According to this as-
sumption our metals and our metalloids are simple modifi-
cations of a single substance, probably hydrogen, the atoms
thereof forming different molecular groupings. In the present
state of science, these ideas, as yet purely hypothetical, can
be passed by ; and relying for the present on the great laws
of Dal ton, Ampere, Dulong, and Petit, we have the right to
consider the simple bodies of contemporary chemistry as repre-
senting groups of atoms identical among themselves in each
simple body, but specifically different from one simple body
to another. Now each of these atomic species has its individual
energy, its own affinities. In the group of the other atomic
species it has friends, it has indifferents, it has enemies. It
willingly unites itself to the first, neglects the second, refuses,
on the contrary, to combine with the last. Moreover, this faculty
of attracting and of being attracted attains in each atomic
species a different degree of energy. Whence we may conclude
that there are in the different atomic species differences of mass
and of form. In aggregating themselves thus, according to their
affinities, atoms arrange themselves into small systems, having in
each body a special structure. These atomic systems are called

The atoms of alkaline metals, such as potassium and sodium,

6 BIOLOGY. [BooK r.

cannot fix each more than one atom of chlorine or of bromine ;
they are monoatomic, as, for instance, hydrogen. Calcium, barium,
strontium, in order that their attractive power may be saturated,
need to fix two atoms of chlorine ; they are diatomic, as, for
instance, oxygen. Phosphorus, which in the perchlorure of
phosphorus succeeds in fixing five atoms of chlorine, is pentatomic.

It is these inequalities in the mode and the power of combina-
tion, in the capacity of saturation, which we call the atomicity of
each atomical species, designating specially by that expression
the maximum capacity of saturation. However, hereby is by no
means implied that a pentatomic species, for instance azote, can-
not combine with less than five atoms. Azote, which fixes five
atoms in the chlorohydrate of ammonia (AzH 4 Cl), is not more
than triatomic in ammoniac gas (AzH 3 ), and is only diatomic in
the bioxide of azote. For the sake of greater clearness, the
denomination atomicity is reserved to designate the capacity of
absolute saturation. The capacities of inferior saturations are
called quantivalences. Thus then azote is pentatomic, but it is
trivalent in gas ammoniac, and so on.

This notion of atomicity has thrown a great light on the
ultimate texture of bodies, and also on the march hither and
thither of atoms in various combinations. In effect, free or
combined, every atom tends to saturate itself by the annexion of
other atoms. If, for instance, a tetratomic atom has combined
with two atoms only, it ceases not to tend to saturate its attrac-
tive force ; it strives to fix two atoms more. But these two
atoms once found, no other simple body can combine with our
tetratomic atom, unless by displacing one or two of its atoms
and becoming their substitute. If, for instance, we take from
a carburet of saturated hydrogen an atom of hydrogen, the
molecule thus mutilated can unite itself to an atom of chlorine.
But the chlorine is monoatomic ; this, however, does not hinder
it from fixing the complex molecule of the carburet, impoverished
to the extent of an atom of hydrogen. The reason is that
certain atomic groups, certain molecules, can play in combina-
tions the part of a single atom. They are what we call com-


pound radicals. This notion of compound radicals has a pre-
dominant importance in the chemistry of organic substances, so
called because nearly altogether they constitute the substance
of living bodies. It simplifies extremely their apparent com-
plexity. It is thus that, according to Mulder, the formula of
albumineis l<XC w H 81 N 5 O u )+8 8 Pk If we limit ourselves to
totalising the atoms, this formula gives C 400 H 310 N 50 120 + S 2 Ph,
a molecule of frightful complication. But if we admit a com-
pound radical, proteine (C 40 H 31 N 5 12 ), comporting itself as a
simple atom, the molecular structure of albumine is enormously
simplified : it approaches that which we are accustomed to meet
in the chemistry called mineral. It is probably also from this
notion of compound radicals that we must seek the explanation
of what has been called isomeria. If bodies having the same
elementary composition, such as the tartaric and paratartaric,
malic acid, citric acid, sugars, gums, have nevertheless distinctive
properties, we must probably attribute the dissimilarities to
differences of molecular structure, to the existence, in the very
heart of these isomeric bodies, of dissimilar compound radicals.

There is another notion not less important than that of com-
pound radicals for the easy comprehension of the formulas of
the chemistry called organic, the notion, namely, of autosatura-
tion. In effect, the atomicity of a simple body does not always
expend itself on atoms of a different species ; it may manifest
itself between atoms of the same species. The atoms of carbon,
for instance, can saturate themselves. An atom of carbon, which


is tetratomic, c , may, by expending merely a quarter of its

atomicity, unite itself with another atom of carbon, which, in its
turn, will neutralise in this combination a quarter of its attrac-
tive energy ; there will result thus therefrom a molecule hexa-
valent, that is to say, capable of still enchaining six atoms :

l l

c c


Let a third atom of carbon then unite itself to this molecule,
we have an octovalent molecule :

I l I

c c c

Finally, the adjunction of a fourth atom of carbon gives a
decavalent compound :

c c c c

This notion of autosaturation has enabled us to systematise a
quantity of facts of organic chemistry, to create rationally new
compounds, to classify and to seriate groups. We ow T e to it the
theory of alcohols, and that of hydrocarburets. 1

The preceding pages contain the principal notions of general
chemistry, which as we proceed we propose to apply. We must,
however, before ending this chapter say a few words on what
have been called catalyses. Certain bodies brought into contact
with other bodies determine by their presence alone, and without
taking any other part in the reactions, either combinations or
metamorphoses or unfoldings. It seems as if in these cases the
body, intervening, by its presence alone, brings into play an attrac-
tive force sufficient to disturb the atomicity of the body which it
influences, without, however, being able to enter into combination
with that body. For instance, platina determines, by its presence
alone, the combination of oxygen and hydrogen, the formation
of water; it transforms also alcohol into acetic acid by deter-
mining its oxidation.

These are catalyses of combination.

The albuminoidal substances introduced into the stomach
impregnate themselves there with gastric juice, expand, and in

1 Consult for further details, Wurtz, Philosophie Chimique, Chimie nouvdlc,
etc. Haquet, article, Atomique (Theorie) in the Encyclopedic Generate.


consequence the organic substance of the gastric juice achieves
in these alimentary substances an isomeric 'modification, which
renders them liquid, absorbable, in short, transforms them into
albuminose. In the same way, under the influence of sulphuric
acid diluted, cane-sugar, cellulose, gums, and fecules are metamor-
phosed first of all into dextrine, and then into glycose, or grape-

These are isomeric catalyses.

The hippuric acid of the urines of herbivorous animals
unfolds itself, under the 'influence of the mucous elements
modified by the air, into hippuric acid and sugar of gelatine or

That is an unfolded catalysis.

In sum, the universe must be regarded as a whole composed
of atoms dissimilar, and variously grouped according to their
affinities. These active atoms are the foundation, the substance,
the cause of all things : to use the expression of Tyndall, they
are giants travestied.

The various aspects of bodies result from the various modes
of aggregation of the constituent elements.

" All the changes accomplished on the surface of the globe are
due to combinations which are made or to combinations which
are unmade." l

All chemical phenomena are consequently the expression of
atomic combinations, and can be included in four general

1. Simple change of molecular structure, or isomeria.

2. Unfolding of compound molecules.

3. Adjunction, addition of atoms, or of molecules not yet
saturated, or, inversely, subtraction of atoms.

4. Substitution of certain atoms, certain molecules for others
in a compound body.

These general characteristics manifestly exclude all ulti-
mate, all radical difference between living organised bodies and

1 Dumas, Traiti de Chimie, t. viii.


inorganic bodies. Is there sufficient reason, however, for distin-
guishing between an inorganic world and an organic world?
What are the dissimilar qualities of these two grand groups?
This is what we propose to examine in the following

[Note. When in this chapter atoms are spoken of as
full, it is in the sense of a plenum excluding a vacuum.






IP, as results from the preceding exposition, the universe is a
whole eternally unstable in form, eternally immutable in sub-
stance, it follows as a matter of course that living or organised
bodies cannot be constituted of aught essentially special. An
integrant part of the medium which environs them, they come
forth from it only to return to it, and there is not an atom of
their substance which does not participate of the eternity of
universal matter, the basis of everything which exists. There
is not one of these atoms which has not played an infinite
number of parts in an infinity of organic and anorganic com-
binations, and which is not destined to play an infinite number
more. Also, in analysing elementarily the most complex of
animals, man, we, in normal conditions, find in him only four-
teen simple bodies of mineral chemistry, the list of which is
herewith given :












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