984 



THE CENTRAL NERVOUS SYSTEM 



According to Dolley, there is, as a result of continued activity, at 

 first a steady increase of the basic chromatic material. This increase 

 ttects first the extra-nuclear chromatin, the Nissl substance, which, 

 according to the most modern view, is really nuclear substance distri- 

 buted through the cytoplasm and functions as such (Goldschmidt). 

 The size and number of the granules are increased, and some of the 

 chromatic material is diffused throughout the cytoplasm, as indicated 

 by diffuse staining. Then the intranuclear chromatin also undergoes 

 an increase, and the size of the cell is increased too. In moderate 

 activity the change goes no farther. At this stage the cell is hyper- 

 chromatic i.e., as compared with a normal resting cell it contains an 



Fig. 398. Effect of Fatigue on Nerve-Cells (Barker, after Mann). Two motor 

 cells from lumbar cord of dog fixed in sublimate and stained with toluidin 

 blue, a, from rested dog; i, pale nucleus; 2, dark Nissl spindles; 3, bundles 

 of nerve fibrils, b, from fatigued dog; 4, dark shrivelled nucleus; 5, pale 

 spindles. 



excess of chromatin. The production of chromatin having reached the 

 maximum of which the nucleus is capable, and functional activity, 

 which entails the using up of the extranuclear chromatin, still continu- 

 ing, the total chromatin content begins to diminish, first in the nucleus, 

 through the passage of its chromatin into the cytoplasm to recruit the 

 Nissl substance, then in the cytoplasm as well. Accompanying the 

 disappearance of the chromatic material there is diminution in the size 

 of both cell and nucleus, but especially of the nucleus, so that the normal 

 proportion between volume of cell and volume of nucleus (nucleus- 

 plasma relation of Hertwig) is disturbed in favour of the cytoplasm. 

 Both cell and nucleus become irregular in outline or crenated. Later 



