THE NERVE CELL 121 



arc found throughout the gray matter of the central portion and in the 

 peripheral ganglia of the cerebrospinal division and in the sympathetic 

 ganglia. Nerve fibers occur in the white matter of the central portion 

 and in the nerve trunks and ganglia of the peripheral portions of the 

 nervous system. 



In the peripheral nervous system the nervous tissues are chiefly 

 supported by the connective tissues, but in the central portion a special 

 form of supporting tissue, the neuroglia, is also found. This is de- 

 scribed below. 



THE NERVE CELL 



(Cyton, Cell Body, Perikaryon, Ganglion Cell) 



This term, as already stated, includes the cell body with its den- 

 drons and the proximal portion of its long axon. The cell bodies vary 

 in size from 4 / to 200 ft in diameter. Their shape is chiefly dependent 

 upon the number of their dendritic processes. Unipolar nerve cells, with 

 but a single process, are flask-shaped or pyriform; bipolar cells, whose 

 processes are usually derived from opposite extremities, are most fre- 

 quently fusiform; multipolar nerve cells, from the considerable number 

 of their processes, are irregularly stellate. 



Nucleus. The cytoplasm of the cell is finely granular and contains 

 a large vesicular nucleus which, as a rule, is excentrically situated. The 

 appearance of this large nucleus is quite characteristic of the nerve cell 

 as distinguished from the cells of other tissue. The nuclear membrane 

 is distinct and highly chromatic. The contents of the nucleus, however, 

 except for the large spherical nucleolus which is quite constantly present, 

 is noticeably deficient in chromatin. Those few small karyosomes which 

 are present are mostly adherent to the inner surface of the nuclear mem- 

 brane. The achromatic nucleoplasm forms the greater portion of the 

 nucleus. Occasionally the chromatin forms still finer granules, and is 

 more equally distributed throughout the nucleus. A large, chromatic, 

 centrally situated nucleolus is nearly always present. 



Cytoplasm. The finer structure of the cytoplasm of the nerve cell 

 is the subject of considerable difference of opinion. The studies of 

 Xissl have shown that it is divisible into a substance which is readily 

 stained by methylene blue, thionin, etc. (the stainable substance of Nissl, 

 tigroid of von Lenhossek), and an apparently homogeneous substance 

 which is not so readily stained (the unstainable substance of Nissl). 



