SECTION II. 

 NERYOUS SYSTEM. 



CHAPTER I. 



GENERAL STRUCTURE AND FUNCTIONS OF THE 

 NERYOUS SYSTEM. 



Ix entering upon the study of the nervous system, we commence 

 the examination of an entirely different order of phenomena from 

 those which have thus far engaged our attention. Hitherto we 

 have studied the physical and chemical actions taking place in the 

 body and constituting together the process of nutrition. We have 

 seen how the lungs absorb and exhale different gases; how the 

 stomach dissolves the food introduced into it, and how the tissues 

 produce and destroy different substances by virtue of the varied 

 transformations which take place in their interior. In all these 

 instances, we have found each organ and each tissue possessing 

 certain properties and performing certain functions, of a physical 

 or chemical nature, which belong exclusively to it, and are charac- 

 teristic of its action. 



The functions of the nervous system, however, are neither phy- 

 sical nor chemical in their nature. They do not correspond, in 

 their mode of operation, with any known phenomena belonging to 

 these two orders. The nervous system, on the contrary, acts only 

 upon other organs, -in some unexplained manner, so as to excite or 

 modify the functions peculiar to them. It is not therefore an appa- 

 ratus which acts for -itself, but is, intended entirely for the purpose 

 of influencing, in an indirect manner, the action of other organs. 

 Its object is to connect" and associate the functions of different 



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