NERVE-CELLS. 4:7 



Large, irregularly-shaped nmltipolar cells, with numer- 

 ous prolongations, are found chiefly in the anterior cornua 

 of the gray matter of the spinal cord, and have been called 

 motor cells. These sometimes present as many as ten or 

 twelve poles. . 



With all these differences in the size and form of the 

 nerve-cells, they present tolerably uniform general charac- 

 ters as regards their structure and contents. Leaving out 

 the apolar and unipolar cells, the perfectly-developed cells 

 are of an exceedingly irregular shape, with strongly-refract- 

 ing, granular contents, frequently a considerable number of 

 pigmentary granules, and a distinct nucleus and nucleolus. 

 The nucleus in the adult is almost invariably single, though, 

 in very rare instances; two have been observed. Cells with 

 multiple nuclei are often observed in young animals. The 

 nucleoli are usually single, but there may be as many as four 

 or five. The strongly-refracting contents, the peculiar shape, 

 and the poles or prolongations give the nerve-cells an ex- 

 ceedingly characteristic appearance, which is represented in 

 Fig. 7. ' 



The diameter of the cells is as variable as their form. 

 They usually measure from I2 1 go to -g^-g- of an inch ; 1 but 

 there are many of larger size, and some are smaller. The 

 nuclei measure from 2 ^ 0() to I2 1 go of an inch. 



The nerve-cells are so delicate and prone to alteration 

 that their study is exceedingly difficult. Sections of the 

 nerve-centres must be prepared with great care, and are not 

 easily made and preserved. In the numerous anatomical 

 investigations that have been made within the last few years, 

 the centres have generally been hardened artificially ; and 

 almost every investigator has used different processes and 

 reagents, which may account in a measure for the differ- 

 ences of opinion that now exist on all points connected with 

 the minute anatomy of these parts. 



There is at the present time considerable discussion with 



1 POUCHET, Precis d'histologie humaine, Paris, 1864, p. 139. 

 104 



