EVOLUTION AND MUTABILITY OF LIVING MATTER AND BRUTE MATTER.
Supposed immobility of brute bodies—Mobility and mutability of the
sidereal world.—§ 1. The movement of particles and molecules in brute
bodies—The internal movements of brute bodies—Kinetic conception of
molecular motion—Reality of the motion of particles—Comparison of the
activity of particles with vital activity.—§ 2. Brownian movement—Its
existence—Its character—Its independence of the nature of the bodies
and of the nature of the environment—Its indefinite duration—Its
independence of external conditions—The Brownian movement must be the
first stage of molecular motion.—§ 3. Motion of particles—Migration of
material particles—Migration under the action of weight; of diffusion;
of electrolysis; of mechanical pressure.—§ 4. Internal activity of
alloys—Their structure—Changes produced by deforming agencies—Slow
return to equilibrium—Residual effect—Effect of annealing; effect of
stretching—Nickel steel—Colour photography—Conclusion—Relations of the
environment to the living or brute matter.
One of the most remarkable characteristics of a living being is its
evolution. It undergoes a continuous change. It starts from something
very small; it assumes a configuration and grows; in most cases
it declines and disappears, having followed a course which may be
predicted—a sort of ideal trajectory.
_Supposed Immobility of Brute Bodies._—It may be asked whether this
evolution, this directed mobility, is so exclusively a feature of the
living being as it appears, and if many brute bodies do not present
something analogous to it. We may answer in no uncertain tones.
Bichat was wrong when he contrasted in this respect brute bodies with
living bodies. Vital properties, he said, are temporary; it is their
nature to be exhausted; in time they are used up in the same body.
Physical properties, on the contrary, are eternal. Brute bodies have
neither a beginning nor an inevitable end, neither age, nor evolution;
they remain as immutable as death, of which they are the image.
_Mobility and Mutability of the Sidereal World._—This is not true,
in the first place, of the sidereal bodies. The ancients held the
sidereal world to be immutable and incorruptible. The doctrine of
the incorruptibility of the heavens prevailed up to the seventeenth
century. The observers who at that epoch directed towards the heavens
the first telescope, which Galileo had just invented, were struck with
astonishment at discovering a change in that celestial firmament which
they had hitherto believed incorruptible, and at perceiving a new star
that appeared in the constellation Ophiuchus. Such changes no longer
surprise us. The cosmogonic system of Laplace has become familiar to
all cultivated minds, and every one is accustomed to the idea of the
continual mobility and evolution of the celestial world. “The stars
have not always existed,” writes M. Faye; “they have had a period of
formation; they will likewise have a period of decline, followed by
final extinction.”
Thus all the bodies of inanimate nature are not eternal and immutable;
the celestial bodies are eminently susceptible of evolution, slow
indeed with that we observe on the surface of our globe; but this
disproportion, corresponding to the immensity of time and of cosmic
spaces as compared with terrestrial measurements, should not mislead us
as to the fundamental analogy of the phenomena.
§ 1. THE MOVEMENT OF PARTICLES AND MOLECULES IN BRUTE BODIES.
It is not only in celestial spaces that we must search for that
mobility of brute matter which imitates the mobility of living matter.
In order to find it we have only to look about us, or to inquire from
physicists and chemists.
As far as geologists are concerned, M. le Dantec tells us somewhere of
one who divided minerals into _living rocks_—rocks capable of change
of structure, of evolution under the influence of atmospheric causes;
and _dead rocks_—rocks which, like clay, have found at the end of all
their changes a final state of repose. Jerome Cardan, a celebrated
scientist of the sixteenth century, at once mathematician, naturalist,
and physician, declared not only that stones live, but that they suffer
from disease, grow old, and die. The jewellers of the present day use
similar language of certain precious stones; the torquoise, for example.
The alchemists carried these ideas to an extreme. It is not necessary
here to recall the past, to evoke the hermetic beliefs and the dreams
of the alchemists, who held that the different kinds of matter lived,
developed, and were transmuted into each other.
I refer to precise and recent data, established by the most expert
investigators, and related by one of them, Charles Edward Guillaume,
some years ago, before the _Société helvétique des Sciences
naturelles_. These data show that determinate forms of matter may
live and die, in the sense that they may be slowly and continuously
modified, always in the same direction, until they have attained an
ultimate and definitive state of eternal repose.
_The Internal Movements of Bodies._—Swift’s reply to an idle fellow who
spoke slightingly of work is well known. “In England,” said the author
of _Gulliver’s Travels_, “men work, women work, horses work, oxen work,
water works, fire works, and beer works; it is only the pig who does
nothing at all; he must, therefore, be the only gentleman in England.”
We know very well that English gentlemen also work. Indeed, everybody
and everything works. And the great wit was nearer right than he
supposed in comparing men and things in this respect. Everything is at
work; everything in nature strives and toils, at every stage, in every
degree. Immobility and repose in the case of natural things are usually
deceptive; the seeming quietude of matter is caused by our inability
to appreciate its internal movements. Because of their minuteness we
do not perceive the swarming particles that compose it, and which,
under the impassible surface of the bodies, oscillate, displace each
other, move to and fro, and group themselves into forms and positions
adapted to the conditions of the environment. In comparison with these
microscopic elements we are like Swift’s giant among the Lilliputians;
and this is far from being a sufficiently forcible comparison.
_Kinetic Conception of Molecular Motion._—The idea of this peculiar
form of motion is by no means new to us. We were familiarized with
it in scientific theories during our school days. The atomic theory
teaches us that matter behaves, from a chemical point of view, as if it
were divided into molecules and atoms. The kinetic theory explains the
constitution of gases and the effects of heat by supposing that these
particles are endowed with movements of rotation and displacement.
The wave theory explains photic phenomena by supposing peculiar
vibratory movements in a special medium—the ether. But these are merely
hypotheses which are not at all necessary; they are the images of
things, not the things themselves.
_Reality of the Motion of Particles._—Here there is no question of
hypotheses. This internal agitation, this interior labour, this
incessant activity of matter are positive facts, an objective reality.
It is true that when the chemical or mechanical equilibrium of bodies
is disturbed it is only restored more or less slowly. Sometimes days
and years are required before it is regained. Scarcely do they attain
this relative repose when they are again disturbed, for the environment
itself is not fixed; it experiences variations which react in their
turn upon the body under consideration; and it is only at the end of
these variations, at the end of their respective periods, that they
will attain together, in a universal uniformity, an eternal repose.
We shall see that metallic alloys undergo continual physical and
chemical changes. They are always seeking a more or less elusive
equilibrium. Physicists in modern times have given their attention to
this internal activity of material bodies, to the pursuit of stability.
Wiedemann, Warburg, Tomlinson, MM. Duguet, Brillouin, Duhem, and
Bouasse have revived the old experimental researches of Coulomb and
Wertheim on the elasticity of bodies, the effects of pressures and
thrusts, the hammering, tempering, and annealing of metals.
The internal activity manifested under these circumstances presents
quite remarkable characteristics which cannot but be compared to the
analogous phenomena presented by living bodies. Thus have arisen even
in physics, a figurative terminology, and metaphorical expressions
borrowed from biology.
_Comparison of the Activity of Particles with Vital Activity._—Since
Lord Kelvin first spoke of the _fatigue_ of metals, or the _fatigue_
of elasticity, Bose has shown in these same bodies the fatigue of
electrical contact. The term _accommodation_ has been employed in the
study of torsion, and according to Tomlinson for the very phenomena
which are the inverse of those of fatigue. The phenomena presented by
glass when acted on by an external force which slowly bends it, have
been called facts of adaptation. The manner in which a bar of steel
resists wire-drawing has been compared to _defensive_ processes against
threatened rupture. And M. C. E. Guillaume speaks somewhere of “the
heroic resistance of the bar of nickel-steel.” The term “defence” has
also been applied to the behaviour of chloride or iodide of silver when
exposed to light.
There has been no hesitation in using the term “memory” concurrently
with that of hysteresis to designate the behaviour of bodies acted
on by magnetism or by certain mechanical forces. It is true that
M. H. Bouasse protests in the name of the physico-mathematicians
against the employment of these figurative expressions. But has he not
himself written “a twisted wire is a wound-up watch,” and elsewhere,
“the properties of bodies depend at every moment upon all anterior
modifications”? Does not this imply that they retain in some manner the
impression of their past evolution? Powerful deformative agencies leave
a trace of their action; they modify the body’s condition of molecular
aggregation, and some physicists go so far as to say that they even
modify its chemical constitution. With the exception of M. Duhem, the
disciples of the mechanical school who have studied elasticity admit
that the effect of an external force upon a body depends upon the
forces which have been previously acting on it, and not merely upon
those which are acting on it at the present moment. Its present state
cannot be anticipated, it is the recapitulation of preceding states.
The effect of a torsional force upon a new wire will be different from
that of the same force upon a wire previously subjected to torsions
and detorsions. It was with reference to actions of this kind that
Boltzmann, in 1876, declared that “a wire that has been twisted or
drawn out remembers for a certain time the deformations which it has
undergone.” This memory is obliterated and disappears after a certain
definite period. Here then, in a problem of static equilibrium, we find
introduced an unexpected factor—time.
To sum up, it is the physicists themselves who have indicated the
correspondence between the condition of existence in many brute bodies
and that in many living bodies. It cannot be expected that these
analogies will in any way serve as explanations. We should rather
seek to derive the vital from the physical phenomenon. This is the
sole ambition of the physiologist. To derive the physical from the
vital phenomenon would be unreasonable. We do not attempt to do this
here. It is nevertheless true that analogies are of service, were it
only to shake the support which, from the time of Aristotle, has been
accorded to the division of the bodies of nature into _psuchia_ and
_apsuchia_—_i.e._, into living and brute bodies.
§ 2. THE BROWNIAN MOVEMENT.
_The Existence of the Brownian Movement._—The simplest way of judging
of the working activity of matter is to observe it when the liberty of
the particles is not interfered with by the action of the neighbouring
particles. We approximate to this condition when we watch, through the
microscope, grains of dust suspended in a liquid, or globules of oil
suspended in water. Now what we see is well known to all microscopists.
If the granulations are sufficiently small, they seem to be never at
rest. They are animated by a kind of incessant tremor; we see the
phenomena called the “Brownian movement.” This movement has struck
all observers since the invention of the magnifying glass or simple
microscope. But the English botanist, Brown, in 1827, made it the
object of special research and gave it his name. The exact explanation
of it remained for a long time obscure. It was given in 1894 by M.
Gouy, the learned physicist of the Faculty of Lyons.
The observer who for the first time looks through the microscope at
a drop of water from the river, from the sea, or from any ordinary
source—that is to say, water not specially purified—is struck with
surprise and admiration at the motion revealed to him. Infusoria,
microscopic articulata, and various micro-organisms people the
microscopic field, and animate it by their movements; but at the same
time all sorts of particles are also agitated, particles which cannot
be considered as living beings, and which are, in fact, nothing but
organic detritus, mineral dust, and debris of every description. Very
often the singular movements of these granulations, which simulate up
to a certain point those of living beings, have perplexed the observer
or led him to erroneous conclusions, and the bodies have been taken for
animalcules or for bacteria.
_Characters of this Movement._—But it is as a rule quite easy to avoid
this confusion. The Brownian movement is a kind of oscillation, a
stationary, dancing to-and-fro movement. It is a Saint Vitus’s dance
on one and the same spot, and is thus distinguished from the movements
of displacement customary with animate beings. Each particle has its
own special dance. Each one acts on its own account, independently of
its neighbour. There is, however, in the execution of these individual
oscillations a kind of common and regular character which arises from
the fact that their amplitudes differ little from each other. The
largest particles are the slowest; when above four thousandths of a
millimetre in diameter, they almost cease to be mobile. The smallest
are the most active. When so small as to be barely visible in the
microscope, the movement is extremely rapid, and can only occasionally
be perceived. It is probable that it would be still more accelerated in
smaller objects; but the latter will always escape our observation.
_Its Independence of the Nature of the Bodies and of the
Environment._—M. Gouy remarked that the movement depends neither on the
nature nor on the form of the particles. Even the nature of the liquid
has but little effect. Its degree of viscosity alone comes into play.
The movements are, indeed, more lively in alcohol or ether, which are
very mobile liquids; they are slow in sulphuric acid and in glycerine.
In water, a grain one two-thousandth of a millimetre in diameter
traverses, in a second, ten or twelve times its own length.
The fact that the Brownian movement is seen in liquors which have been
boiled, in acids and in concentrated alkalies, in toxic solutions of
all degrees of temperature, shows conclusively that the phenomenon
has no vital significance; that it is in no way connected with vital
activity so called.
_Its Indefinite Duration._—The most remarkable character of this
phenomenon is its permanence, its indefinite duration. The movement
never ceases, the particles never attain repose and equilibrium.
Granitic rocks contain quartz crystals which, at the moment of their
formation, include within a closed cavity a drop of water containing
a bubble of gas. These bubbles, contemporary with the Plutonian age
of the globe, have never since their formation ceased to manifest the
Brownian movement.
_Its Independence of External Conditions._—What is the cause of this
eternal oscillation? Is it a tremor of the earth? No! M. Gouy saw the
Brownian movement far away from cities, where the mercurial mirror of
a seismoscope showed no subterranean vibration. It does not increase
when the vibrations occur and become quite appreciable. Neither is
it changed by variation in light, magnetism, or electric influences;
in a word, by any external occurrences. The result of observation
is to place before us the paradox of a phenomenon which is kept up
and indefinitely perpetuated in the interior of a body without known
external cause.
_The Brownian Movement must be the First Stage of Molecular
Motion._—When we take in our hands a sheet of quartz containing a
gaseous inclusion, we seem to be holding a perfectly inert object. When
we have placed it upon the stage of the microscope, and have seen the
agitation of the bubble, we are convinced that this seeming inertia is
merely an illusion.
Repose exists only because of our limited vision. We see the objects as
we see from afar a crowd of people. We perceive them only as a whole,
without being able to discern the individuals or their movements.
A visible object is, in the same way, a mass of particles. It is a
molecular crowd. It gives us the impression of an indivisible mass, of
a block in repose.
But as soon as the lens brings us near to this crowd, as soon as the
microscope enlarges for us the minute elements of the brute body,
then they appear to us, and we perceive the continual agitation of
those elements which are less than four thousandths of a millimetre
in diameter. The smaller the particles under consideration, the more
lively are their movements. From this we infer that if we could
perceive molecules, whose probable dimensions are about one thousand
times less, their probable velocity would be, as required by the
kinetic theory, some hundreds of metres per second. In the case of
objects we can only just see, the Brownian velocity is only a few
thousandths of a millimetre per second. No doubt, concludes M. Gouy,
the particles that show this velocity are really enormous when compared
with true molecules. From this point of view the Brownian movement
is but the first degree, and a magnified picture of the molecular
vibrations assumed in the kinetic theory.
§ 3. THE INTERNAL ACTIVITY OF BODIES.
_Migration of Material Particles._—In the Brownian movement we
take into account only very small, isolated masses, small free
fragments—_i.e._, material particles which are not hampered by their
relations to neighbouring particles. Any one but a physicist might
believe that in true solids endowed with cohesion and tenacity, in
which the molecules were bound one to the other, in which form and
volume are fixed, there could be no longer movements or changes. This
is a mistake. Physics teaches us the contrary, and, in late years
especially, has furnished us characteristic examples. There are real
migrations of material particles throughout solid bodies—migrations
of considerable extent. They are accomplished through the agency
of diverse forces acting externally—pressures, thrusts, torsions;
sometimes under the action of light, sometimes under the action of
electricity, sometimes under the influence of forces of diffusion.
The microscopic observation of alloys by H. and A. Lechatelier, J.
Hopkinson, Osmond, Charpy, J. R. Benoit; researches into their physical
and chemical properties by Calvert, Matthiessen, Riche, Roberts Austen,
Lodge, Laurie, and C. E. Guillaume; experiments on the electrolysis
of glass, and the curious results of Bose upon electrical contact of
metals, show in a striking manner the chemical and kinetic evolutions
which occur in the interior of bodies.
_Migration under the Action of Weight._—An experiment by Obermeyer,
dating from 1877, furnishes a good example of the motions of solid
bodies through a hardened viscid mass, taking place under the influence
of weight. The black wax that shoemakers and boatbuilders use, is a
kind of resin extracted from the pine and other resinous trees, melted
in water, and separated from the more fluid part which rises from it.
Its colour is due to the lampblack produced by the combustion of straw
and fragments of bark. At an ordinary temperature it is a mass so hard
that it cannot always be easily scratched by the finger-nail; but if it
is left to itself in a receptacle, it finally yields, spreads out as
if it were a liquid, and conforms to the shape of the vessel. Suppose
we place within a cavity hollowed out of a piece of wood a portion of
this substance, and keep it there by means of a few pebbles, having
previously placed at the bottom of the cavity a few fragments of some
light substance, such as cork. The piece of wax is thus between a light
body below and a heavy body above. If we wait a few days, this order
is reversed—the wax has filled the cavity by conforming to it; the
cork has passed through the wax and appears on the surface, while the
stones are at the bottom. We have here the celebrated experiment of the
flask with the three elements, in which are seen the liquids mercury,
oil, and water superposed in the order of their density, but in this
case demonstrated with solid bodies.
_Influence of Diffusion._—Diffusion, which disseminates liquids
throughout each other, may also cause solids to pass through other
solids. Of this W. Roberts Austen gave a convincing proof. This
ingenious physicist placed a little cylinder of lead upon a disc of
gold, and kept the whole at the temperature of boiling water. At this
temperature both metals are perfectly solid, for the melting point of
gold is 1,200° C., and of lead is 330°. Still, after this contact has
been prolonged for a month and a half, analysis shows that the gold has
become diffused through the top of the cylinder of lead.
_Influence of Electrolysis._—Electrolysis offers another no less
remarkable means of transportation. By its means we may force metals,
such as sodium or lithium, through glass walls. The experiment may be
performed as indicated by M. Charles Guillaume. A glass bulb containing
mercury is placed in a bath of sodium amalgam, and a current is then
made to pass from within outward. After some time it can be shown that
the metal has penetrated the wall of the bulb, and has become dissolved
within it.
_Influence of Mechanical Pressure._—Mechanical pressure is also capable
of causing one metal to pass into another. We need not recall the
well-known experiment of Cailletet, who, by employing considerable
pressure, caused mercury to sweat through a block of iron. In a more
simple manner W. Spring showed that a disc of copper could be welded
to a disc of tin by pressing them strongly one against the other. Up to
a certain distance from the surfaces of contact a real alloy is formed;
a layer of bronze of a certain thickness unites the two metals, and
this could not take place did not the particles of both metals mutually
interpenetrate.
§ 4. INTERNAL ACTIVITY OF ALLOYS.
_Structure of Alloys._—Metallic alloys have a remarkable structure,
which is essentially mobile, and which we have only now begun to
understand by the aid of the microscope. Microscopical examination
justifies to a certain degree Coulomb’s conjecture. That illustrious
physicist explained the physical properties of metals by imagining them
to be formed of two kinds of elements—integral particles, to which
the metal owes its elastic properties, and a _cement_ which binds the
particles, and to which it owes its coherence. M. Brillouin has also
taken up this hypothesis of duality of structure. The metal is supposed
to be formed of very small, isolated, crystalline grains, embedded in
an almost continuous network of viscous matter. A more or less compact
mass surrounding more or less distinct crystals is the conception which
may be formed of an alloy.
_Changes of Structure produced by Deforming Agencies._—It has been
shown that profound changes of crystalline structure can be produced
by various mechanical means, such as hammering, and the stretching
of metallic bars carried to the point of rupture. Some of these
changes are very slow, and it is only after months and years that
they are completed, and the metal attains the definite equilibrium
corresponding to the conditions to which it is exposed. Though there
may be discussions concerning the extent of the transformations to
which it is subjected, though some believe they affect the chemical
condition of the alloy, while others limit its power to physical
effects, it is nevertheless true—and this brings us back to our
subject—that the mass of these metals is at work, and that it only
slowly attains the phase of complete repose.
_The Slow Re-establishment of Equilibrium. Residual Effect._—These
operations by which the physical characters of metals are changed, and
by which they are adapted to a variety of industrial needs—compression,
hammering, rolling, stretching, and torsion—have an immediate, very
apparent effect; but they have also a consecutive effect, slowly
produced, much less marked and less evident. This is the “residual
effect,” or “Nachwirkung” of the Germans. It is not without importance,
even in practical applications.
Heat also creates a kind of _forced equilibrium_. This becomes but
slowly modified, so that a body may remain for a long time in a state
which is, however, not the most stable for the conditions under which
it is considered. The number of these bodies _not in equilibrium_ is as
great as that of the substances which have been exposed to fusion. All
the Plutonic rocks are in this condition. Glass presents a condition of
the same kind. Thermometers placed in melting ice do not always mark
the zero Centigrade. This displacement of the zero point falsifies all
records if care is not taken to correct it. The correction usually
requires prolonged observation. The theory of the displacement of the
thermometric zero is not entirely established; but we may suppose,
with the author of the _Traité de Thermométrie_, that in glass, as
in alloys, are to be found compounds which vary according to the
temperature. At each temperature glass tends to assume a determinate
composition and a corresponding state of equilibrium; but the previous
temperature to which it has been subjected clearly has an influence
on the rapidity with which it attains its state of repose. The effect
of variation is more marked when we observe glass of more complicated
composition. We can understand that those which contain comparable
quantities of the two alkalies, soda and potash, may be more subject to
these modifications than those having a more simple composition based
on a single alkali.
_Effects of Annealing._—A piece of brass wire that has been drawn and
then heated is the scene of certain very remarkable internal changes,
and these have been only recently recognized. The violent treatment
of the metallic thread in forcing it through the hole in the die has
crushed the crystalline particles; the interior state of the wire is
that of broken crystals embedded in a granular mass. Heating changes
all that. The crystals separate, repair themselves, and are built
up again; they are then hard, geometrical bodies, in an amorphous,
relatively soft and plastic mass; their number keeps on increasing;
equilibrium is not established until the entire mass is crystallized.
We may imagine how many displacements, enormous when compared with
their dimensions, the molecules have to undergo when passing through
the resisting mass, and arranging themselves in definite places in the
crystalline structures.
In the same way, too, in the manufacture of steel, the particles of
coal at first applied to the surface pass through the iron.
This _faculty of molecular displacement_ enables the metal in some
cases to modify its state at one point or another. The use made of this
faculty under certain circumstances is very curious, greatly resembling
the adaptation of an animal to its environment, or the methods of
defence against agents that might destroy it.
_Effect of Stretching. Hartmann’s Experiment._—When a cylindrical
rod of metal, held firmly at either end—a test-piece, as it is
called in metallurgy—is pulled sufficiently hard, it often elongates
considerably, part of the elongation disappearing as soon as the strain
ceases, and the other part remaining. The total elongation is thus the
sum of an “elastic elongation,” which is temporary, and a “permanent
elongation.” If we continue the stretching, there appears at some point
of the rod a local extension with contraction of sectional area. It is
here that the rod will break.
But in place of continuing the stretching, Mr. Hartmann suspends it.
He stops, as if to give the “metal-being” time to rally. During this
delay it would seem that the molecules hasten to the menaced point
to reinforce and harden the weak part. In fact the metal, which was
soft at other points, at this spot looks like tempered metal. It is no
longer extensible.
When the experimenter begins the stretching again after this rest, and
after the narrowed bar has been rolled and become cylindrical again,
the local extension and sectional contraction is forced to occur at
another point. If another rest is given at this point the metal will
also become hardened.
If we repeat the experiment a sufficient number of times, we shall find
a total transformation of the rod, which becomes hardened throughout
its entire extent. It will break rather than elongate if the stretching
is sufficiently severe.
_Nickel Steels—their “Heroic” Resistance._—Nickel steels present this
phenomena in an exaggerated degree. The alternation of operations which
we have just described, bringing the various parts of an ordinary
steel rod into a tempered state, is not necessary with nickel steel.
The effect is produced in the course of a single trial. As soon as
there is any tendency to contraction the alloy hardens at that precise
place; the contraction is hardly noticeable; the movement is stopped at
this point to attack another weak point, stops there again and attacks
a third, and so on; and, finally, the paradoxical fact appears that
a rod of metal which was in a soft state and could be considerably
elongated has now become throughout its whole extent as hard, brittle,
and inextensible as tempered steel. It is in connection with this point
that M. C. E. Guillaume spoke of “heroic resistance to rupture.” It
would seem, in fact, as if the ferro-nickel bar had reinforced each
weak point as it was threatened. It is only at the end of these efforts
that the inevitable catastrophe occurs.
_Effect of Temperature._—When the temperature changes, it is seen that
these ferro-nickel bars elongate or retract, modifying at the same time
their chemical constitution. But these effects, like those which occur
in the glass bulb of a thermometer, do not occur at once. They are
produced rapidly for one part, and more slowly for a small remaining
portion. Bars of ferro-nickel which have been kept at the same
temperature change gradually in length in the course of a year. Can
we find a better proof of internal activity occurring in a substance
differing so greatly from living matter?
_Nature of the Activity of Particles._—These are examples of the
internal activity that occurs in brute bodies. Besides, these facts
that we are quoting merely to refute Bichat’s assertion relative to
the immutability of brute bodies, and to show us their activity, also
afford us another proof. They show that this activity, like that of
animals, wards off foreign intervention, and that this parrying of
the attack, again like that of animals, is adapted for the defence
and preservation of the brute mass. So that if we consider of special
importance the adaptative, teleological characteristic of vital
phenomena, a characteristic which is so easily made too much of in
biological interpretations, we may also find it again in the inanimate
world. To this end we may add to the preceding examples one more which
is no less remarkable. This is the famous case of Becquerel’s process
for colour-photography.
_Colour-Photography._—A greyish plate, treated with chloride or iodide
of silver and exposed to a red light, rapidly becomes red. It is then
exposed to green light, and after passing through dull and obscure
tints it becomes green. To explain this remarkable phenomenon, we
cannot improve on the following statement:—The silver salt protects
itself against the light that threatens its existence; that light
causes it to pass through all kinds of stages of coloration before
reducing it; the salt stops at the stage which protects it best. It
stops at red, if it is red light that assails it, because in becoming
red by reflection it best repels that light—_i.e._, it absorbs it the
least.
It may then be advantageous, for the comprehension of natural
phenomena, to regard the transformation of inanimate matter as
manifestations of a kind of internal life.
_Conclusion. Relations of the Surrounding Medium to the Living Being
and the Brute Body._—Brute bodies, then, are not immutable any more
than are living bodies. Both depend on the medium that surrounds them,
and they depend upon it in the same way. Life brings together, brings
into conflict, an appropriate organism and a suitable environment.
Auguste Comte and Claude Bernard have taught us that vital phenomena
result from the reciprocal action of these two factors which are
in close correlation. It is also from the reciprocal action of the
environment and the brute body that inevitably result the phenomena
which that body presents. The living body is sometimes more sensitive
to variations of the ambient medium than is the brute body, but at
other times the reverse is the case. For example, there is no living
organism as impressionable to any kind of stimulus whatever as the
bolometer is to the slightest variations of temperature.
There can only be, then, one chemically immutable body—namely, the atom
of a simple body, since, by its very definition, it remains unaltered
and intangible in combinations. This notion of an unalterable atom
has, however, itself been attacked by the doctrine of the ionization
of particles due to Sir J. J. Thomson; and besides, with very few
exceptions—those of cadmium, mercury, and the gases of the argon
series—the atoms of simple bodies cannot exist in a free state.
Thus, as in the vital struggle, the ambient medium by means of
alimentation furnishes to the living being, whether whole or
fragmentary, the materials of its organization and the energies which
it brings into play. It also furnishes to brute bodies their materials
and their energies.
It is also said that the ambient medium furnishes to the living being
a third class of things, the _stimuli_ of its activities—_i.e._, its
“provocation to action.” The protozoon finds in the aquatic environment
which is its habitat the stimuli which provoke it to move and to absorb
its food. The cells of the metazoon encounter in the same way in the
lymph, the blood, and the interstitial liquids which bathe them, the
shock, the stimulus which brings their energies into play. They do not
derive from themselves, by a mysterious spontaneity without parallel in
the rest of nature, the capricious principle which sets them in motion.
Vital spontaneity, so readily accepted by persons ignorant of biology,
is disproved by the whole history of the science. Every vital
manifestation is a response to a stimulus, a provoked phenomenon. It
is unnecessary to say this is also the case with brute bodies, since
that is precisely the foundation of the great principle of the inertia
of matter. It is plain that it is also as applicable to living as to
inanimate matter.