THE NERVE CELL 



123 



Nissl's substance, chromophilic 

 or tigroid substance, occurs in the 

 form of flake-like granules of vary- 

 ing size and irregular shape. Their 

 disposition within the cytoplasm is 

 subject to considerable variations 

 in different nerve cells, but accord- 

 ing to Nissl it is fairly constant in 

 cells of the same location for any 

 given species. The amount also of 

 the chromophilic substance is sub- 

 ject to variation depending upon, 

 the functional condition of the in- 

 dividual. It has been shown that 

 the substance is greatly diminished 

 by fatigue (Dolly) and after sur- 

 gical shock (Crile). In general 

 also, the longer the axon the great- 

 er the amount of chromophilic sub- 

 stance. Chemically, it is a nucleo- 

 proteid. There is considerable his- 

 tologic evidence to indicate that it 

 has a nuclear origin, appearing 

 first in the form of 'chromidia/ 

 and it is accordingly sometimes 

 designated as cytochromatin. Miihl- 

 man has shown, however, that 

 tigroid nuclein is soluble in weak 

 soda solutions while nucleus nu- 

 clein is not. It has been suggested 

 (Heidenhain) that it may perhaps 

 have an accessory nuclear function. 

 According to Held it is present as 

 a diffuse continuous substance, co- 

 agulated in the form of flakes and 

 granules in fixed tissues. 



Those nerve cells in which the 

 Nissl substance is abundant are 

 said to be in a pyknomorphous, 

 those in which it is scanty in an 



FIG. 136. PYRAMIDAL MULTIPOLAR 

 NERVE CELL FROM THE CEREBRAL 

 CORTEX OF A MOUSE. 



a, axon; d, dendrons; c, collaterals. 

 Golgi technic. (Barker, after Ramtfn 

 y Cajal.) 



