XVlll INTRODUCTION. 



experiences, all the phenomena which it presents, all the 

 combinations and decompositions which take place in it, 

 result from the^ji. Chymistry can foresee and explain 

 the consequences of their action. She can even pro- 

 duce, by her exertions, new combinations. 



In addition to the laws of affinity, which govern inor- 

 ganic matter, living bodies are subject to other laws, 

 which continually modify the action of the first. These 

 laws of vitality are energetic, and govern the law of 

 affinity in proportion to the perfect organization of the 

 body. It is this, which causes the mode of action in living 

 bodies to escape our researches ; so that, although wit- 

 nesses of all which passes in these bodies, we can neither 

 explain nor imitate their productions. The science of 

 chymistry is limited to a knowledge of the substances 

 which enter into animals and vegetables, to serve them 

 for nourishment; and to the study of all the agents 

 which aid them in the performance of their functions. 

 She knows what these bodies appropriate to their use, 

 and what they reject. But the mode of elaboration 

 by their organs, the formation of their products, and the 

 manner of their growth, is, and must for a long time be, 

 a mystery to us. That which we already know of the 

 functions of living bodies, is much ; but that of which we 

 are ignorant, far exceeds it. 



The laws of vitality, like all the other laws of nature, 

 are unchangeable. But their action is varied in living 

 bodies by a difference in organization ; in the same 

 manner as the products vary in each species, and in 

 each one of their organs. It is this variety of productions 

 which surprises us, — especially when we consider, that 

 their form and their quality are constantly renewed every 

 year, and with every generation. 



