INTRODUCTION 3 



*No matter how far we delve into the phenomena per- 

 taining to Hving beings, we are always confronted with the 

 same question which was propounded in ancient days, at 

 the very beginning of Science: Is life due to a power, a 

 special force, or is it only a modality of the general forces 

 of nature? In other words, does life contain a special force 

 which is distinct from the physical, chemical, or mechanical 

 forces? The Vitalists have always claimed the impossibility 

 of explaining physically or mechanically all the phenomena 

 of life. Their opponents have always answered by giving 

 well-proven physico-chemical explanations to an ever- 

 increasing number of vital manifestations. We must admit 

 that the latter have constantly gained ground. Will they 

 succeed in explaining everything by their theories, or in 

 spite of their efforts will there not remain a quid proprium 

 of life which will always be irreducible? 



'This is the point that must be examined, for, far from 

 being only of philosophical interest, it is, on the contrary, 

 capable of showing us to what degree the fundamental 

 problems of all biology are dominated by chemical and 

 physical methods. 



'There are two classes of nutritional phenomena which 

 essentially constitute life and which are the origin, without 

 exception, of all its manifestations. One of these, organic 

 destruction or disassimilation, can already be classified 

 among the chemical actions. These decompositions in 

 living beings are no more mysterious than those which take 

 place in organic substances. As to the second class, the 

 phenomena of organizing genesis and nutritional regenera- 

 tion, they appear at first glance to be of a quite distinct vital 

 nature, and often irreducible to general chemical actions. 

 This, however, only appears to be so, and these phenomena 

 must be considered under the double aspect of an ordinary 

 chemical synthesis and of an organic evolution in progress. 

 Indeed, vital genesis incorporates phenomena of chemical 

 synthesis arranged and developed according to a particular 

 order which constitutes their evolution. It is important to 



