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THE CENTRAL NERVOUS SYSTEM 



mass, from which they can be separated, leaving merely the neuropile, 

 through which, however, the reflex continues to be conveyed. After a 

 time, of course in this case also the reflex disappears, because 

 an axon can not live indefinitely after it has been separated from its 

 nerve cell. 



These facts regarding the general function of the nerve cell arouse 

 our curiosity as to its morphological structure. When nerve cells are 

 fixed and stained in various ways they show certain elements in the 



Fig. 209. Part of an anterior cornwal cell from the calf's spinal cord, stained to show neurofibrils. 

 a.r, axon; a, b, c, dendrites. (From Bethe.) 



cytoplasm namely, (1) large granules or masses, which stain deeply 

 with basic dyes and are called Nissl bodies (Fig. 208), and (2) a fine 

 network of fibrils passing through the cell substance from one process or 

 dendrite to another neurofibrils (Fig. 209). These appearances in fixed 

 and stained preparations are possibly, however, entirely artificial ; for when 

 nerve cells are preserved in a living state by being suspended in some of 

 the animal's own lymph or blood serum it is found, when they are ex- 

 amined by the aid of the ultramicroscope (see page 52), that the cytoplasm 



