NERVE TISSUE 135 



sents the same appearance ("equivalent picture"), and that this appearance 

 furnishes a norm for comparison with cells showing pathological changes, and 

 which have been subjected to the same technic. 



Many nerve cells contain more or less brownish or yellowish 

 pigment (Fig. 75). This pigment, which is a lipochrome, is not 

 present in the cells of the new-born, but appears in increasing 

 amounts with age. Its significance is not known. Another black 

 pigment known as melanin is present in certain cells in the central 

 nervous system {e.g., the substantia nigra). This pigment is said 

 to increase in amount until adolescence. 



Fig. 79. — Golgi Cell Type II. from Cerebral Cortex of Cat. (KoUiker.) x, Coarse 

 protoplasmic processes with gemmules easily distinguishable from the more delicate, 

 smoother axone, a. The latter is seen breaking up into a rich plexus of terminal fibres 

 near its cell of origin, practically the entire neurone being included in the drawing. 



In addition to its characteristic structure, the nerve cell may 

 contain many elements found in other cells (p. 46). Golgi, Holm- 

 gren, Cajal, and others have also demonstrated a network of canals 

 within the nerve cell similar to that found in other cells (p. 47, Fig. 4). 



n. The Protoplasmic Processes or Dendrites. — These have a 

 structure similar to that of the cell body, consisting of neurofibrils, 

 perifibrillar substance, and, in somatochrome cells, chromophilic 

 bodies (Figs. 75 and 76). Dendrites branch dichotomously, become 



