THE NERVE ELEMENTS. 



i;; 



In the cells controlling the most distal segments of a 

 limb, the disproportion between cell-body and neuron is 

 even greater, since the cell-body is smaller and the neuron 

 longer than in the example chosen. On the other hand, 

 there are within the central system cells the neurons of 

 which are so short that they probably have a volume 

 even less than that of the cell-body. 



So far as the matter 

 has been studied, it ap- 

 pears that cells of small 

 diameter have neurons 

 of small diameter, while 

 cells of large diameter 

 generally have neurons 

 of large diameter, but 

 often the relations are 

 by no means propor- 

 tional. The two parts 

 of the cell therefore 

 vary in the same sense, 

 but the variations are 

 not strictly interdepen- 

 dent. Having deter- 

 mined that the volume 

 of the nerve clement 



does increase with age, FIG. 26. A cell with a short neuron 

 it is desirable to also S ivin - off man y bran ches. 

 determine the manner 

 in which this occurs. 

 Kaiser's study of the 



In 



such a cell the neuron is less in 

 volume than the cell-body. This 

 is the extreme form of the '* cen- 

 tral cell." (Ramon y Cajal.) D, 

 dendrons ; N, neuron. 



cervical enlargement of 



the spinal cord illustrates this in part, although the 



measurements were made on the largest cell-bodies only. 1 



1 Kaiser, Die Funktionen der Ganglienzellcn des Halsmarkes, 

 Haag, 1891. 



