564 SIGNIFICANCE OF THE NERVOUS SYSTEM 



allied to chromatin which are scattered through the cytoplasm and also extend 

 into the larger dendrites but not into the axon. They are generally designated 

 as Nissl's granules or tigroid bodies; (3) strands of denser protoplasm which 

 traverse the cytoplasm in all directions making connections between the different 

 processes of the neuron. They do not invade the nuclear substance. These 

 so-called fibrillffi are said to be continuous with the fib rill ae composing the axis- 

 cylinder, and are regarded as the specific conducting element of the neuron. 



To be sure, these characteristics are not shown by all nerve-cells, 

 because some of them possess very small amounts of cytoplasm; 

 while others appear to be composed solely of nuclear material. Nissl 1 



^ -*"" -^" sS> <&* tas>--T 



Hgjr^ 



tJ^f^^^W^ 



- --^gfesr 





' 



FIG. 280. NORMAL NERVE CELL FROM THE LOBUS ELECTRICUS OF THE TORPEDO. (Garten.) 



who has made an exact study of the structural details of the different 

 nerve-cells, divides them into: 



1. Somachrome Cells. The cytoplasm surrounding the nucleus, exhibits a dis- 

 tinct structure, showing thereby that it possesses a decided functional importance. 

 By far the largest number of nerve cells belong to this group. They may be sub- 

 divided further in accordance with the staining qualities of their cytoplasm. 2 



2. Cytochrome Cells. Their cell-bodies are poorly developed, so that they 

 seem to be composed of naked nuclei. Cells of this kind are present in the sub- 

 stantia gelatinosa of Rolando and in the granular layer of the cerebellum and olfac- 

 tory lobe. 



1 Allg. Zeitschr. fur Psychiatric, liv, 1897, 101. 



2 Barker. The Nervous System, New York, 1899, 121. 



