ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 449 



Having now treated of these general points which apply 

 more or less fully to nerve cells wherever found, the ques- 

 tion naturally follows, what are the special functions of the 

 various nerve centers found in the body, and what are 

 the specific paths of the fibers connecting these centers 

 with each other and with the periphery ? We are therefore 

 concerned next with the finer architecture of the central 

 nervous system. 



THE FINER ARCHITECTURE AND THE SPECIAL PHYSIOLOGY 

 OF THE CENTRAL NERVOUS SYSTEM. 



Perhaps in no department of the field of physiology 

 have the views been so materially modified of late as in the 

 conceptions of the structure of the central nervous system. 

 Recent studies of such men as Golgi, Van Gehuchten, 

 Ramon y Cajal, and others have completely changed our 

 notions of the fundamental structure of nervous tissue. It 

 is now believed, and with the best of evidence, that the 

 entire nervous system is made up of separate and distinct 

 units called neurons, a general description of which occurred 

 in the preceding pages. 



These neurons are practically all alike, at least ana- 

 tomically, unless we except those of the cerebrum to which 

 we are at present obliged to assign psychic functions. No 

 neuron is connected with any other neuron directly, but the 

 impulse from one to another is effected at the point where 

 they lie either close together or in possible direct contact. 

 The old notion of a continuous network of nerve fibers per- 

 vading the entire system is done away with. 



In such separate and distinct neurons the cell body is 

 the physiological and nutritive center. To this center im- 

 pulses are carried by some of its branches, and from it in 

 turn impulses are carried out by other branches. A section 

 of any of the branches or nerves of such a neuron at once 

 results in the death of that end of the nerve severed from 

 the cell body. It is the purpose in this paragraph to show 

 in an elementary way but with some special detail the man- 

 ner in which these neurons are arranged and superposed. 

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