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THE NERVOUS SYSTEM 



these neurofibrillae have on our accepted theories of nerve function, other than 

 that they are assumed to be the conducting elements. 



The Neurone Theory. Our knowledge of the function of the nerv- 

 ous system is best explained on the basis of the neurone theory, which 

 considers the nerve cell as a physiological unit. By this view each gross 

 division of the nervous system is supposed to consist of a large number of 

 individual neurones, each of which is a more or less complete morphological 

 unit capable of carrying on certain functions of its own. Each of these 

 neurones maintains physiological continuity with its associates, presumably 

 by protoplasmic contact rather than by continuity; so that well-marked paths 

 of conduction are possible throughout the extent of the particular mass of 



FIG. 356. Purkinje Cells from the Cerebellum of the Swallow. A, Taken in the morning; B, 

 taken in the evening. (Hodge.) 



which the neurone is a part, and throughout the adjacent masses. By this 

 view, paths of conduction are made up of series of individual neurones which 

 are in physiological continuity. 



The Characteristics of the Individual Nerve Cell. The function 

 of the nerve cell may be discussed under two headings: The function of the 

 cell body, and the function of the cell processes. 



The cell body of the nerve cell is the part that contains the nucleus and is 

 the center of those activities which influence the metabolism of the cell itself. 

 If the cell body be isolated from its processes, the processes will degenerate, 

 while the body continues to live. In other words, the cell body may be con- 

 sidered as the center of those trophic influences which regulate the nutrition 

 of the processes. Although the nerve cell as a whole is in many, perhap: in 



