g8 LIFE AND DEATH. 



ever proposed in natural philosophy, and the theory 

 least encumbered with hypotheses. It reduces all 

 particular laws to two fundamental principles — that 

 of the conservation of energy, which contains the 

 principles of Galileo and Descartes, of Newton, of 

 Lavoisier, Joule's law, Hess's law, and Berthelot's 

 principle of the initial and final states; and also 

 Carnot's principle, from which are deduced the laws 

 of physico-chemical and chemical equilibrium. These 

 two principles therefore sum up the whole of natural 

 science. They express the necessary relation of all 

 the phenomena of the universe, their uninterrupted 

 gentic connection, and their continuity. 



A priori there would be little likelihood that a 

 doctrine, so universal and so thoroughly verified in 

 the physical world, could be restricted, and thus 

 be useless to the living world. Such a supposi- 

 tion would be contrary to the scientific method, which 

 always tends to the generalization and the explanation 

 of elementary laws. The human mind has always 

 proceeded thus : it has applied to the unknown 

 order of living phenomena the most general laws of 

 contemporary physics. 



This application has been found legitimate, and has 

 been justified by experiment whenever it has been a 

 question of the laws or of the really fundamental or 

 elementary conditions of phenomena. It has, on the 

 other hand, however, been unfortunate when it has 

 stopped short of secondary characteristics. When we 

 now concede the subjection of living beings to these 

 general laws of energetics, we are following a 

 traditional method. There is no doubt that this 

 application is legitimate, and that experiment will 

 justify it a posteriori. 



