30 INTRODUCTION. 



the central masses of the nervous system. There does not 

 exist a single part of the body, which, under certain circum- 

 stances, may not be the seat of some sensation. When the ani- 

 mal has received a sensation, and that excites in him a voli- 

 tion, it is also through the nerves that this volition is trans- 

 mitted to the muscles, the contractions of which produce the 

 movements of the animal. 



The nervous action is not confined to transmitting the im- 

 pressions received by the senses and the volition to the mus- 

 cles; for, the nervous central masses are also the organs of in- 

 stinct and of the cerebral functions. 



The functions of which we speak are not only superadded 

 in animals to the organic or vegetative functions, but they sin- 

 gularly modify the exercise of the latter. Thus in nutrition, 

 the introduction of the aliments is generally produced by mus- 

 cular movements; the muscular fibres which form a coat to 

 the intestines, is also the cause that the aliment they contain is 

 moved on in this tube; it is also a set of muscles, which, in 

 many animals, are placed at the point and centre of reunion 

 of all the vessels, which propel the blood; and it is muscles 

 also which induce, by their movement, the introduction into 

 and diffusion of air in the respiratory organ. There are 

 senses placed at the entrance of the organs of nutrition. 

 Nerves are also distributed to the organs of nutrition, and al- 

 though in an ordinary state these nerves transmit neither 

 sensation nor volition, and movements are suddenly deter- 

 mined in them by impressions or irritations, nevertheless, in 

 powerful affections of the nervous centres, the movements are 

 interrupted, and in a pathological state these functions are ac- 

 companied with sensations. Generation is like nutrition, mo- 

 dified in its actions by the animal functions. 



15. There is, in fact, between all the organs, and between 

 all the functions of animals, a connexion which exists in all 

 organized and living bodies, but which is still more remarka- 

 ble in animals, and especially in some of them. In organized 

 beings, which possess only nutrition and reproduction, the 

 latter of these functions is the consequence of the former. 

 In animals which enjoy motion and sensation, nutrition must 



