106 



THE NEEVOUS TISSUES 



Nissl's substance, or tigroid, occurs in the form of flake-like 

 granules of varying size and irregular shape. Their disposition 

 within the cytoplasm is subject to considerable variations in dif- 



FIG. 103. NERVE CELL FROM THE OLFACTORY BULB OF A RABBIT. 



An arkyochrome nerve cell in the parapyknomorphous condition. Highly 



magnified. (After Nissl.) 



ferent nerve cells. Yet it has been found that nerve cells occu- 

 pying the same position in any given animal species always present 

 the same type of structure as regards the disposition of their Nissl 

 granules. According to Nissl, the following types may be distin- 

 guished : 



A. SOMATOCHKOME NEEYE CELLS, in which the nucleus is sur- 

 rounded by a considerable cytoplasmic body. 



1. Ar Icy o chrome nerve cells, whose stainable substance occurs in 

 the form of an irregular network. These cells are widely distrib- 

 uted among the sensory nuclei of the spinal cord and medulla. 



2. Stichochrome nerve cells, whose stainable substance presents 

 a linear arrangement, the rows of granules being more or less nearly 



