CHAPTER IV. 



OF LIFE. 



Life has long been the mystery of mysteries ; and in modern 

 times it has been the last refuge, the citadel of supematuralism. 

 In fact, so long as there were no clear ideas regarding the con- 

 stitution of bodies, or the composition of chemical aggregates, so 

 long as so-called organic substances appeared radically different 

 from mineral substances, it was impossible to unravel the 

 mystery of life. We now know that organised bodies do not 

 contain a material atom which was not first derived from, and 

 aftei-wards restored to, the exterior medium. We have made an 

 enumeration of the immediate principles which constitute living 

 bodies ; we have been able to reproduce a certain number of 

 these in our chemical laboratories. We know in what physical 

 state, under what blended conditions, they are found within 

 organised and living bodies. We know, moreover, that the 

 entire universe contains an always active matter, that what 

 is called force cannot sever itself from what is called matter, 

 that consequently there can no longer be any question of a 

 vital principle, of an archeus, superadded to living beings, and 

 regulating their phenomena. Even these simple general facts 

 authorise us to affirm that vital phenomena are simply the result 

 of the properties of living matter. To give a just idea of life, 

 it remains to us then to determine what are its properties, and 

 also what are the principal conditions of their manifestation. 



We prove then, first of all, that life depends strictly upon the 

 exterior medium, that an alteration in the composition of the 



