96 



THE NERVE TISSUE 



NucleKS. ^The large spherical nucleus is bounded by a distinct 

 nuclear membrane. Within it is a large nucleolus which stains 

 intensely with basic dyes. The chromatic material within the 

 nucleus is generally scant, as compared with that of other cells. 

 In large cytons it appears as a network concentrated about the 

 nucleolus. Fine protoplasmic granules staining with both basic and 

 acid dyes occur abundanth'. In some neurons several nucleoli may 

 be observed. Mature neurons differ from other cells in that they 

 do not undergo mitosis. 



Nissl Bodies.— These irregular masses of basophilic material 

 occurring in the cytoplasm have been called tigroid bodies, chromo- 

 phil substance, and other names. (Fig. 52.) S])ecial techniques 



Fig. 52.— Spinal ganglion cells of the cat, showing numerous Nissl bodies. Each 

 cell is surrounded by a number of smaller satellite cells. 



are often used to make them stand out clearly, but almost e\ery 

 stained preparation shows them scattered through the cytoplasm. 

 It is belie^'ed that these bodies contain iron and store oxygen, and 

 that their presence is essential to the functioning of the nerve cell. 

 Their appearance as definite bodies nvA\ be due to fixation, since 

 different fixatives result in differences in their form. In the 

 living cells the substance of which they are com])ose(l may be in a 

 diffuse state. ]\Iodifications in their appearance occur with changes 

 in the conditions of the nerve cells. In pathological conditions they 

 often disappear entirely. 



