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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



only the creations of our own thought, meaning 

 that they are definitions of names, or agreed terms 

 for shortening speech ; but he recognizes primi- 

 tive words that are understood without any need 

 of defining them. 



Now, the word life is in that situation. All 

 men understand each other when they speak of 

 life and death. It would be impossible, at any 

 rate, to separate these two terms, or these two 

 correlative ideas, for that which lives is that 

 which will die, and that which is dead is that 

 which has been alive. When we are dealing 

 with a phenomenon of life, as with any phenome- 

 non of Nature, the first condition is, to under- 

 stand it ; its definition can only be given a poste- 

 riori — it is the conclusion gathered from a previ- 

 ous study ; but, properly speaking, such a propo- 

 sition is not a definition, it is a view, a concep- 

 tion. Our business, then, will be to learn what 

 conception we should shape for ourselves of the 

 phenomena of life, at this day, in the present state 

 of our physiological knowledge. 



That conception has varied, as a matter of 

 course, with epochs and in accordance with the 

 advance of knowledge. At the beginning of this 

 century a French physiologist, Le Gallois, pub- 

 lished, even at that date, a volume of experiments 

 on the principle of life, and the seat of that prin- 

 ciple. We are now no longer looking for the seat 

 of life ; we know that it dwells everywhere, in 

 all the molecules of organized matter. The vital 

 properties are in reality only in the living cells, 

 and all the rest is merely arrangement and mech- 

 anism. The very various manifestations of life 

 are expressions, combined and diversified in many 

 thousands of ways, of fixed and unchanging or- 

 ganic elementary properties. Therefore it is of 

 less consequence to know the immense variety 

 of vital manifestations which Nature seems unable 

 even to exhaust, than it is to fix with rigorous 

 precision the properties of tissues that give rise to 

 them. At this day, for this reason, all the efforts 

 of science are directed to the histological study 

 of those infinitely little points which conceal the 

 true secret of life. 



How deeply soever we may now be able to 

 penetrate into the secrets of those phenomena 

 peculiar to living beings, the question rising for 

 solution is always the same. It is the very ques- 

 tion asked in the oldest times, at the beginning of 

 science. Is life due to a special power, or force, 

 or is it only a mode of action of the general forces 

 of Nature ? In other words, does there exist in liv- 

 ing beings a peculiar force, distinct from physi- 

 cal, chemical, or mechanical forces ? The vital- 



ists have always taken up their position in the im- 

 possibility of explaining all the phenomena of life 

 through physics or mechanics ; their opponents 

 have always answered by bringing an increasing 

 number of vital manifestations within well-demon- 

 strated physico-chemical explanations. It must 

 be owned that the latter have steadily gained 

 ground, and that especially in our times they gain 

 more and more every day. Will they thus suc- 

 ceed in reducing everything to their theories, and 

 will there not remain, spite of all their efforts, a 

 quid proprium of life, still irreducible ? This is 

 the point we now have to examine. By carefully 

 analyzing all vital phenomena, whose explanation 

 belongs to physical and chemical forces, we shall 

 press vitalism back into a region of smaller ex- 

 tent, and therefore more easily defined. 



Of the two orders of nutritive phenomena that 

 substantially compose life, and originate all its 

 manifestations, without exception, there is one, 

 that of destruction, of organic disassimilation, 

 which henceforward takes its place unquestion- 

 ably among chemical actions ; these decomposi- 

 tions in living beings present no greater nor less 

 mystery than do those shown us by inorganic bod- 

 ies. As to the phenomena of organizing through 

 genesis, and of renovation through nutrition, 

 they do seem at the first glance to be of an entire- 

 ly special vital nature, not reducible to general 

 chemical action. This, however, is only so in ap- 

 pearance, and to account for the matter com- 

 pletely we must study these phenomena under the 

 twofold aspect they present, that of an ordinary 

 chemical synthesis, and of an organic evolution 

 which is proceeding. In truth, vital genesis com- 

 prises phenomena of chemical synthesis arranged 

 and unfolded after a special order, which makes 

 their evolution. It is necessary to distinguish 

 chemical phenomena in themselves from their evo- 

 lution, for these are two completely separate 

 things. In so far as they are synthetic acts, it is 

 clear that these phenomena arise only from gen- 

 eral chemical forces ; and this is plainly proved 

 by studying them one by one in their succession. 

 The calcareous matters found in the shells of mol- 

 lusks, the eggs of birds, the bones of mammals, are 

 very certainly formed during the evolution of the 

 embryo according to the laws of common chemis- 

 try. The fatty and oily matters, too, are formed 

 in the same way, and chemistry has already suc- 

 ceeded in the artificial reproduction in its labora- 

 tories of a large number of immediate principles 

 and essential oils which naturally belong to the 

 animal or vegetable kingdom. So, too, amylace- 

 ous substances that are developed in animals, and 



