Popular Science Monthly/Volume 45/August 1894/Form and Life
|←Modern Views and Problems of Physics||Popular Science Monthly Volume 45 August 1894 (1894)
Form and Life
By Georges Pouchet
|On Accuracy in Observation→|
By M. GEORGES POUCHET.
IN the first glance over Nature, everything living, every plant or animal, and every part of what lives, seems to have a definite shape; and we are naturally led to regard form in organized beings as an essential attribute of life. On the other hand, gases, which spread out into infinity; liquids, molding themselves on the walls of the vessels that stop their flow; rocks, cut into a thousand shapes without ceasing to be the same rock — show us an inorganic world almost wholly freed from the fatality of form. Crystals, indeed, seem to form an exception to this. They also have limited shapes, with contours even much better defined than those of life; but when we bray them in a mortar, they are still always the same body, and the same chemical species, even though they are no longer crystals. A living being, sugar cane or beet root, rasped or reduced to pulp, has no longer anything of itself. It has ceased to be, and no power can, from the pulp, build the organism back into its former shape. But we can reconstruct the crystal, and draw it anew from its dust.
The living being, considered in itself, independently of the being from which it is derived and those which will be derived from it, is, in its way, with some exceptions, a sort of atom, an indivisible whole. Hence that very just denomination of individual, to designate the being endowed with life.
What we call species in speaking of plants and animals is 522 THE POPULAR SCIENCE MONTHLY.
really only the grouping made in our mind of all the living indi- viduals exhibiting the same form, and which we believe to be all united under a common parentage.
Yet form can not serve of itself to characterize life, for there exist other bodies than crystals in the inorganic world which are individuals. The planets and the rings of Saturn will at once occur as examples. We might also range in the same category comets and whirls of smoke, which are likewise individuals, and cease to be by the mere fact of their division or dissociation.
Form is therefore not sufficient to characterize the living indi- vidual. Let us see if the general features and external aspect of organized beings will not offer us marks to distinguish them from mineral bodies. The plane faces, the sharp edges, and the definite angles of crystals, and the spherical contours of the heavenly bodies, have been contrasted with the undulating surfaces, the less geometrical and more softly defined profiles of plants and animals. This trait is certainly not destitute of value, and the untrained mind is rarely deceived by it. Sometimes the lapidary, in cutting agate, uncovers delicate arborescent shapes in the trans- parency of the gem. The illusion is vi^id, and one might fancy he had a petrified moss under his eyes. A lens will assure him that there is no vegetable fossil here, and will reveal an assem- blage of crystalline needles that have nothing in common with the delicate articulations and waving lines of a genuine moss.
Its particular stamp is so clearly impressed on each living be- ing and on each of its parts, and it is so recognizable that it guides the naturalist with certainty, even when he affirms, from the smallest remnant or weakest impression, the existence on the sur- face of the globe, in prodigiously distant times, of beings that lived then, and with which he is unacquainted. Some of the or- ganisms have left only traces, and he affirms that life passed there, without knowing whether it was vegetable or animal.
The ancients, although they had not our experience in inter- preting the true nature of fossils, never failed to recognize the factory mark which Nature impresses on its works. Science then gave no means of discerning in ammonites the shell of an animal allied to the squids and cuttlefish ; but the finders had at least the feeling that these things had lived, and, by analogy, thej'- saw in them the bones of animals preserved in the earth.
Form is not an essential attribute of life. There exist living beings destitute of living form, as there exist chemical substances that do not crystallize. The microscope reveals in stagnant water gelatinous masses that change their form and move incessantly. "We see a part of the mass stretch out like a foot advancing. Then the whole being seems to pass into this prolongation, which is proportionately swelled out. Another expansion occurs at an-
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other point, and the viscous drop, changing shape continually, seems to flow along slowly. If it meets any vegetable matter, it envelops it, and the stuff suffers a real digestion. The residue is cast out, as it was absorbed, by any point of the surface. We call these beings amo&bas. They are capable of multiplication by division, and every part of them is susceptible of being indif- ferently surface or inside, the drawing part or the part drawn, mobile all at once. For the amoeba can choose its direction and find more light or more darkness according to what we may call its aspirations, since it acts, definitively, as a living being.
If we open a tan vat in the spring, we shall discover here and there irregular golden-yellow filaments, soft and slimy. We ob- serve them changing their place and flowing like the amoDbas. They appear to be seeking one another in the mass of tan, for in the summer, after a shower, they may be seen to join, then rise in the shape of a kind of yellow cake, large and thick as the two hands ; jbhe botanists call them rinjxomyceta, or the slimy fungus. Detach a part of this mass, put it on a potsherd, and it will, like the amoeba, extend branchy expansions, pass itself upon them, stretch out and return upon itself in changing lumps, to be suc- ceeded soon by new stretchings.
We see in these, beings without form, without organs, com- posed solely of an opaque substance, and highly colored in the myxomycetes, but transparent in the amoeba, a little denser than water, with which it does not mix, a substance that moves and feels that is, that shares with us the higher attributes of life. The discovery of the amoebas was at first merely a curiosity till Dujardin and Hugo Mohl, almost at the same time, called atten- tion to a substance entering into the composition of infusoria and the cells of plants that had all the characteristics of the sub- stance of the amoebas. Dujardin called it sarcode ; Hugo Mohl, X)rotoplasma, and that name prevailed. The term, imposed as the name of one of the constituent parts of the vegetable cell, has had the singular fortune to become almost synonymous with matter living or that has lived.
This amorphous substance is the basis of the organism. In plants, it is what in some way builds up every cell, as the worm and the mollusk produce the shell and the tube that protect them, or as the caterpillar envelops itself with the cocoon which it draws out from its glands. So the protoplasm molds around itself the walls of the cell in which it is inclosed. But it is always the prime living part, and when it disappears the cellular wall becomes only an inert body. In animals, likewise, the Qgg, or at least its essen- tial part, the vitellus, shows in its almost universal spherical form the protoplasm shaped at first only by the laws of attraction and resistance common to all "itiatter. But when the egg takes life, the
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first signs it gives of its activity are movements comparable with those of the amoeba. Thus, without effort, we find on different sides life freed from form. We comprehend that it is not essen- tially and fatally bound to form. A body may be living and still have no definite figure. Here the problem is suggested, whether a liquid, a bodily humor, can be living. Is the blood living, like the substance of the nerves or the flesh of the muscles ? It is a deep question and has not yet been answered. At any rate, science has been led for a long time to look for the characteristic of life somewhere else than in form.
The Aristotelians saw a movement in what we call life ; and they gave that name to every change of state of natural bodies as well as to their translation proper in space. Aristotle's treatise on the Soul characterizes life by the three facts of its nourishing itself, developing, and perishing. Growth and decline are changes, and consequently movements; and, as we always see them closely connected with the feeding of the plant as well as of the animal, we find the act of feeding definitively at the basis of the movement which is life. Moreover, do we not see during growth the parts of which the creatures are composed changing places relatively to one another ? Have we not here a clear, absolute distinction from the increase of mineral bodies ?
There are, however, some parts in animals which grow by a simple constant accretion of superadded new particles ; such as the shells of mollusks, even when they are covered by the flesh, like cuttlefish bone. But these forinations, although derived from the organism, are not themselves living. They bear, if we may say so, the stamp and seal of life so far that we can recognize them as a product of it, but no further ; and if they grow, it is as crystals do.
Thomas Aquinas, following Aristotle, gave life the most exact definition that could be made with the knowledge of his time. It is almost as satisfactory for us, for we, too, define life in the same terms. It is a movement, but still not one of the appar- ent though intimate movements to which the Christian encyclo- pedist alludes. It is a molecular movement that escapes our eyes, in the interior of the being, and is revealed to our senses only by its results.
The movement that constitutes lifeisanintimate, profound, in- visible, incessant movement, at once of combination and of decom- position. Living matter is incessantly born and incessantly dying, being formed and suffering destruction all at the same time.
All liquid or gaseous bodies coming in contact with a living substance and soluble by it, penetrate it, mingle with it, and then, carried on in the Avhirl, cease for the most part to be themselves, are transformed, enter into new combifctions that did not exist
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outside of the being, but wbicli are in their turn destroyed and pass into other conditions unsuitable to life, and in which they are cast out to re-enter the inorganic world, which is enriched through them with ammonia, carbonic acid, and oxygen. We are not ac- quainted with the nature of this movement ; we know only that it exists by comparing what goes in and what goes out, and these with the intermediate term, the living substance itself. We know that it is propagated at the same time in all the tissues and all the organs of the being, offering in each a special modality while retaining always the same fundamental character.
This movement is fundamental to the tissues of the living be- ing, from the most simple of them, like the substance of the bone, to the most complex, like that of the muscles or the brain. It is always in the living being, whether it is growing, thriving, or declining toward death, or is attainted with different passional, morbid conditions that might affect it. It is always present in the infinite variety of iDhysiological acts of which our life is made up and which all inevitably lead to an impending molecular modi- fication : the sensation of the retina disturbed by a light-ray, the contraction of a muscle, and even thought. In connection with the last, the effort has been made to reach by tortuous ways the nature of the chemical reactions that necessarily accompany all brain work. Whether this is reached or not, it is impossible to conceive the operation of the nervous elements otherwise than as a phenomenon of nutrition that is, as a modification brought about in the molecular movement.
But we are still unable to penetrate and discover the true na- ture of that inner molecular movement which makes of animated bodies a world apart from the great cosmos. What are the origin and nature of that new energy communicated to inert matter, giv- ing it properties or rather faculties which it had not before, and which are additional to all those with which the chemist and physicist are acquainted ? Let us say, further, that they are added to these without contradicting them, as was believed for a long time when a kind of antagonism was supposed between life and the physico-chemical forces. Life is in no way a triumph over these forces, and they always keep their predominance.
Vital movement is, after all, only an episodical modality of the universal faculty which simple and compound chemical bodies have of reacting upon one another. It requires for its manifesta- tion, like every other reaction, definite conditions, confined within narrow limits, of pressure, temperature, and light.
But the thing we are absolutely ignorant of is the real nature of those inner reactions of which we can not in many cases give the rigorous formula and still less define the thermic equivalent ; the generic quality, as it were, of those movements, at once special
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and infinitely varied, which are going on incessantly in the parts of living bodies. We know that the vital movement in each indi- vidual is to come to an end at a given moment that is death. We have a thousand means of provoking a stoppage of it. We can only propagate it in a certain way when we furnish it, by means of food or generation, with the material substratum neces- sary for its production and development. We can in like man- ner divert it and cause it to produce monsters ; but we have no power to make it appear where it does not exist.
Vital movement is continuous. It was formerly thought pos- sible to suspend it ; that seeds and living beings could die for the moment, and the former keep intact their faculty of germinating, and the latter return to a new existence when placed in favorable conditions. Reviving animals have excited much attention, but little thought has till the present been directed to the supposed suspension of life. In reality, these beings continue to live, but extremely little. The vital movement is not suspended, but is considerably diminished rather than retarded, like the vibration of a sounding cord which loses in intensity till it is no longer heard, while the finger can still feel it tremble. About forty years ago some speculators upon public credulity publicly distributed through all Europe, selling it very dear, a wheat which they said had been taken from a mummy in Egypt, and which when planted gave a prolific return. This was a simple cheat. Yet seeds are known which have retained the germinating faculty a very long time ; they really continue to live, carrying within themselves the inner movement which becomes slower every day and ends with extinction. The seed will inevitably die ; whether it be after a few years or in a century or two makes little difference it will die.
Vital movement is then continuous, but with incessant renew- als, and it also has a very special character. It is propagated in- definitely, while it continually casts off a part of the materials which it had previously animated. That yellowed wheat which the reaper is going to cut, the stubble of which is destined to cover some cottage, the seed of which seems wholly devoted to the support of the life of men, which has to our view not lived a whole year that wheat is eternal ; it has lived through all the past, and may live through all the future. It has dried, but that is only in appearance. Life has not withdrawn from it. Planted next year, it will project a new head, and so on for thousands of years.
We are accustomed to regard as a living being having a kind of beginning and end the head which issues from the seed in the spring, and which autumn will mature. The conception is wholly arbitrary. We really know of no beginning or end to this head. It is not even an individual in the philosophical sense of
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��tlie word ; for it is connected by continuity with all the heads of wheat that preceded it and with all those that will follow it. The important part is the seed, or the germ which it includes, continu- ing itself by a stem and a flower into another seed like it. The root, the straw, the glumes are accessories all to be abandoned every year by the seed incessantly reviving of itself, which veri- tably incarnates the species wheat.
The molecular movement being at the very basis of life, to what extent does it regulate its manifestations ? Does it make its influence felt only to maintain the external form or to exert a cer- tain amount of command upon it ? It does command it in effect, and all the external characteristics of the species and the individ- ual appear to us definitely as subordinated to the conditions of their inner chemistry. Chevreul was the first who formulated the principle of the absolute dependence of life on the physico- chemical laws of inert matter. The demonstration of it is fur- nished in the manure and fertilizers by means of which we suc- ceed in prodigiously modifying the external appearance of the plant, to the point of rendering it almost unrecognizable. This sprout, in a dry, arid soil, is stunted, coriaceous, and hairy ; that other one, from the same kind of seed, growing in the shade, on a soil constantly moist, is large, plump with water, soft and smooth. Without more knowledge, we should see in them two distinct spe- cies, if all the intermediate terms did not meet here and there on grounds half dry or half shaded, to show that we are simply deal- ing with two individuals of the same species, the molecular con- stitution of which is not absolutely identical because of the differ- ent conditions in which each one has lived.
It was long thought that the plant could choose by its roots the substances in the earth useful in its support and growth. This is not correct. The root, in contact with the extremely complex bodies which are continually formed and unformed in the soil around it, takes all those which the spongy terminal tissue of each radicle can dissolve. The plant is in this case only a reagent like any other ; it is passive, and suffers itself to be penetrated by every substance, useful or injurious, in the quantity in which that sub- stance is susceptible of mingling and combining with its super- ficial tissues. By virtue of the molecular constitution of the walls of the root, and especially of the extreme cells of their fibers, plants absorb particular mineral principles, and these principles in their turn, drawn into the vital molecular movement, favor it, impede it, or modify it in some way, and at last provoke a perceptible change in the aspect of the plant. This direct, immediate influ- ence of molecular constitution on the forms of living beings ap- pears to be more sharply marked in plants, but that is perhaps
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because animals have not been so carefully studied with reference to it. Some practices well known to horticulturists demonstrate with a singular evidence this subordination of extreme characters to the chemical composition of living matter as in some of the methods by which new varieties and colors are obtained.
With the aid of analysis and the balance, Prof. Armand Gau- tier exhibits to us these new appearances of plants in relation to the formation of new chemical compounds in them. This has been done under such conditions that it can be said of every ani- mal or vegetable hybrid that it does not represent simply the mingling or the combination of the two forms from which it is derived, but is still more the expression of new molecular combi- nations giving rise to intermediate chemical combinations. We have a right now to affirm that the blood of the mule, in its inti- mate composition, differs as much from, the blood of the horse as from that of the ass.
It is agreed that the different varieties of the European vine are variations of the same species slowly modified under the influ- ence of man. This almost indefinite variation has not only re- sulted in advancing florescence and maturity and in differences in the quantities of tannin, sugar, and coloring matter in the fruit and other parts of the plant. Each of these external changes is in some way only the expression without of certain chemical changes. There appear to be as many kinds of coloring matters of seeds as there are varieties of grapes, and so different that some of them are soluble in water and some not ; some crystallize, oth- ers remain amorphous ; some precipitate the salts of lead in blue, and some in green. In a general way it may be affirmed, from M. Gautier's experiments, that each variety of vine has seen arise in it a new chemical species which would not have existed in Nature any more than the form with which it is associated, if man had not intervened. Man, therefore, in creating hybrids, not only makes new forms, but also throws into Nature chemical principles that had no place there.
The possibility of working in some species of animals the re- markable changes which skill has impressed on the plants of our fields and gardens can hardly be doubted. By depriving an ani- mal of some one of the mineral principles that enter into the com- position of its tissues, we should in all probability greatly modify its external form.
A single experiment is known to us which has been made in this direction by M. Chabry at the marine laboratory of Concar- neau. He selected, as the animal to be experimented upon, the larva of the common sea urchin. It was seen, a few hours after it came out from the egg, as a point moving rapidly in the sea water. Observed under the microscope, it first appeared the shape of a
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bell ; later, it took a strange shape, which was not inappropriately- compared to a lectern. M. Chabry even designated it by the Latin name jpluteus, which means pulpit. As the time for this change of form approaches, there can be seen appearing in the tissues of the young larva a kind of calcareous needles, called spicules, the form and disposition of which are identical in all individuals of the same species. These spicules are composed of the carbonate of lime which the larva finds in the sea water, and which it ab- sorbs as the roots of a plant absorb the potash contained in the soil. This lime traverses the tissues of the larva and collects for a time in them before settling in the half-crystalline figure of the spicules. It may be remarked that although they present a regu- lar arrangement in the larva, the spicules have no relation, at least in the beginning, with the external form or the shape of the organs of the animal.
M. Chabry asked what would happen if he tried by raising the larvae in water destitute of lime to prevent the formation of the spicules. The experiment was not without difficulties. It was necessary to prepare artificially a limeless sea water. With all the pains M. Chabry could take, in the light of the best analysis, the larvae perished in the artificial water as soon as they were hatched. He then tried diminishing by degrees the proportion of lime in the natural water. This lime was the sulphate, and the experiment was directed, in order to prevent too radically chang- ing the water, to substituting another base for calcium. Sodium was taken, because, it being already very abundant in the water, the slight addition of it which it would be necessary to make to replace the lime could not have any great influence. The results were very plain. Without any mixture of lime in the water, the just-hatched larvae were arrested in their development and died in a few hours. If the elimination of calcium is not pushed to its extreme limits, and only a fifteenth part of the already very slight quantity contained in sea water is left, the larvae will not be for forty hours distinguishable from those which are developed in normal water. At the end of that time the spicules should appear while the larva is assuming the form of the pluteus. But in water containing only a fifteenth of the normal calcium this change is not effected. Twenty hours later, in the sixtieth hour of their lives, the larvae are still in the same condition, while those in nor- mal water have spicules already branched, and their having taken the form of the pluteus is marked both by their shape and by the division of their intestine into distinct regions. The larvae de- prived of lime first exhibit this modification of the intestine toward the ninetieth hour, but they have no spicules and have not become pluteus. Their external form has therefore been profoundly af- fected by some change that has been introduced into the inner
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composition of the tissues and the humors through the absence of one of their necessary constituents. The disturbance was not suf- ficient to cause the larvae to perish or to stop the vital movement, but that had been diverted and had resulted in a new configura- tion of the living being. We have made a monster by a chemical process. No doubt a certain number of monstrosities besides those resulting from accidents that have occurred in the course of the development will eventually be attributed to a category of special changes like those which M. Chabry provoked.
A recent discovery has further cast a very striking light on that mysterious relation that connects the chemical constitution of beings with their external form. Aside from the serpents, only a few vertebrate animals are known that distill venom. On the other hand, notwithstanding the deep organic differences that re- move the fishes from the reptiles, we find a few among them the conger, the eel, and the sea eel that have the appearance and almost the form characteristic of snakes. Prof. Mosso has lately shown that the blood of these fishes with the shape of a serpent is poisonous, even very poisonous. Half a thimbleful of eel's blood injected into a dog is enough to cause the animal to fall dead just as if it had been bitten by a rattlesnake. What is the connection between the presence of this poison in the blood of the eel and the shape of its body ?
We may summarize in rigorously scientific language what we have just set forth by saying, with Chevreul and Charles Robin, that the form of living beings is a function of their molecular con- stitution. It is a point to which Darwin and his partisans of the transformist school have not perhaps given sufiicient attention. Everybody now accepts these doctrines in their main features, but they have not taken into account, at least not fully, the factor of the influence of the medium. They have overlooked this chemical necessity which is imposed with every change of form or simply of color. We shall know, as M. Gautier has foreshadowed, the limits of the possible variations of an animal species when we learn how far it lends itself to the creation of new organic compounds. Even when there is nothing more than an exagger- ation of a group of determined organs, a determining modification must be admitted in the chemistry of the individual. If media have been able to act, as everything indicates, it has been only by slow and progressive modification of the molecular constitution of the being, involving inevitably in its turn the changes of ex- ternal configuration that determine each animal or vegetable spe- cies. The transformists show us with complete assurance verte- brated animals descended from some inferior animal, worm, or mollusk. Which ? Here they cease to agree, and every one's preferences are suggested by this or that vague resemblance in
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the disposition of the internal organs. But, if this were ever so much greater, there would still remain something to explain and something of importance. This vertebrate has muscles, organs of senses, viscera like the various animals from which it is sup- posed to have proceeded. But there are, further, in it living sub- stances of a special order, cartilage and bone, which are real chemical species. When, how, and under what circumstances did these substances appear which we find identical as to themselves in all vertebrates which no other existing animals possess ? It is not enough to show us this animal type proceeding from that other, that organ developing itself or disappearing or changing place and relations. We want to be told through what internal chemical actions these organic compounds appeared ; those clear- ly defined substances the presence of which establishes an abso- lute distinction between vertebrate animals and the worms or mollusks from which they are supposed to descend.
Just as the appearance of new chemical compounds hitherto unknown was the necessary condition of the formation of new organic types, so it seems proper to suppose that at the beginning life on our planet aj)pertained only to amorphous masses, which, in a prodigious succession of ages, after incommensurable periods, in consequence of an intimate working in their substance, were succeeded by existences the contours and dimensions of which were gradually and progressively defined. The sense of this necessity, doubtless, haunted M. Haeckel's imagination when he supposed that the Batliyhius was the primordial jelly whence all living beings were derived.
On the other hand, this idea of a simple beginning of life was too far lost sight of by M. F. A. Pouchet and the later champions of the doctrine of spontaneous generation. It is not shown that the question of heterogeneity, which was so exciting thirty years ago, can ever be answered. In any case, it can not be revived under the form which its latest defenders have given it. Their chief error, from which all the others have been derived, was in wishing to overshoot the mark, in seeking to create at the bottom of their matrass, not substance having life a bit of sarcode or protoplasm but a being having a definite form. In the modern idea of the necessities of life, form appears to us as an epiphe- nomenon resulting from infinitely numerous and infinitely pro- gressive circumstances. To sum it all up, form is pre-eminently a hereditary characteristic. It can exist, we can only comprehend it as slowly acquired by a process of modeling a thousand and a thousand times secular. It was this form, this figure, that the partisans of spontaneous generation thought they brought forth in their apparatus ! The objection we raise here, very curiously, was never made to them, and their theory was only ruined by
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detail, by the production of facts undermiinng their experiments, hut which did not touch the foundation of their doctrine. No one will ever cause to appear in a vial, by combining all imaginable elements, a microscopic animal or plant, however simple, with a definite configuration, because that requires duration of existence behind it. The problem to be solved is not there. The necessary thing is to create that unknown molecular movement which alone constitutes life and which brings on all the rest.
At the present time chemists seem to be on the point of obtain- ing by synthesis substances similar to those of which some of the important parts of animals and plants are made ; but we must not nourish a chimerical hope too rapidly. There is a chasm be- tween the end almost reached by M. Schiitzenberger and others, and the creation of the smallest parcel of living matter. One may make albumin like that of an egg, fibrin like that of the blood, but he will still have inert substances, as they are. The white of an egg is not living, although it emanated from a living being, no more than the shell and the greater part of the yolk. It is simply a secretion an outthrow of the living flesh of the hen and which acquires from it nothing more than a composi- tion nearly identical with it, and in any case extremely complex. Hence the difiiculty of reproducing artificially a similar body by the synthesis of the very numerous chemical elements that com- pose its delicate structure. Every molecule must be there and in its place. Even when this synthesis has been performed in his retorts, has the chemist produced life ? Not at all ! He will be like Prometheus in the face of his clay statue ; the fire from heaven will be wanting the living fire. That albumin, that fibrin, the issue of the combination of any number whatever of the different elements that should compose it, remain inert sub- stances.
Yet the thought of producing living matter does not seem en- tirely hopeless. The conditions have already necessarily been realized on the planet, and perhaps many times. It is not impos- sible that at the bottom of the ocean or in stagnant waters sarco- dic masses are still taking spontaneous birth. We have no evi- dence of it, but such a phenomenon does not appear liable to the fundamental objection. How shall we surprise this beginning of life ? If science shall ever succeed in achieving this great work in its laboratories it will have accomplished the desire of the first man of the Mosaic legend. "VVe shall know what life and death are. The dream of the heterogenists will be realized, and man will indeed have created life. Translated for Tlie Popular Science Monthly from the Revue des Deux Mondes.