INTRODUCTION. 21 



therefrom resulting, that animals are capable of executing the 

 innumerable movements that enter into walking and leaping, 

 flight and natation. 



The muscular fibres, appropriated to digestion and the cir- 

 culation, are independent of the will ; they receive nerves, 

 however, but the chief of them are subdivided and arranged 

 in a manner which seems to have for its object their indepen- 

 dence of the ME. It is only in paroxysms of the passions and 

 other powerful affections of the soul, which break down these 

 barriers, that the empire of the me is perceptible, and even 

 then it is almost always to disorder these vegetative functions. 

 It is, also, in a state of sickness only that these functions are 

 accompanied with sensations: digestion is usually performed 

 unconsciously. 



The aliment divided by the jaws and teeth, or sucked up 

 when liquids constitute the food, is swallowed by the muscu- 

 lar movements of the hinder parts of the mouth and throat, 

 and deposited in the first portions of the alimentary canal that 

 is usually expanded into one or more stomachs; there it is 

 penetrated with juices fitted to dissolve it. Passing thence 

 through the rest of the canal, it receives other juices destined 

 to complete its preparation. The parietes of the canal are 

 pierced with pores which extract from this alimentary mass 

 its nutritious portion; the useless residuum is rejected as ex- 

 crement. 



The canal in which this first act of nutrition is performed, 

 is a continuation of the skin, and is composed of similar lay- 

 ers; even the fibres that encircle it are analogous to those 

 which adhere to the internal surface of the skin, called the 

 fleshy pannicle. Throughout the whole interior of this canal 

 there is a transudation which has some connexion with the cu- 

 taneous perspiration, and which becomes more abundant when 

 the latter is suppressed ; the absorption of the skin is even 

 very analogous to that of the intestines. It is in the lowest 

 order of animala that the excrements are rejected by the 

 mouth, their intestines resembling a sac, with but the one 

 opening. 



Even among those where the intestinal canal has two ori- 



