8 7 4 



A MANUAL OF PHYSIOLOGY 



In moderate activity the change goes no farther. At this stage the 

 cell is hyperchromatic i.e., as compared with a normal resting 

 cell it contains an excess of chromatin. The production of chro- 

 matin having reached the maximum of which the nucleus is capable, 

 and functional activity, which entails the using up of the extra- 

 nuclear chromatin still continuing, 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 dis- 

 turbed in favour of the cyto- 

 plasm. Both cell and nucleus 

 become irregular in outline 

 or crenated. Later on, and, 

 it would seem, rather ab- 

 ruptly, swelling of the nucleus 

 and, after some time, of the 

 cytoplasm occurs. This is 



f'^fWV'i \ff/ V*''"HWi : -7 1 / due to oedema, and may be 

 T&SliJ/ vVa\Wi* d taken to indicate an upset 



* 1$5 9-7 \'\ * W'lJf of their normal osmotic rela- 



"'\\iif $ t& \lri ' ' i H ' '/ tions. The earlier occurrence 



'If/ i'if \Y ! V A : '^ of oedema in the nucleus leads 



Vl-rJ i i i \\ ^\ i/J to another change in the nu- 



H.lvf f */ VJV.i-.iii /// cleus-plasma relation, which 



is now disturbed in favour 

 of the nucleus. In the 

 measure in which fatigue 

 progresses the extranuclear 

 chromatic material continues 

 to be used up, and, in spite 

 of its replenishment from the 

 nucleus, it almost or entirely 



FIG. 366. EFFECT OF FATIGUE ON NERVE- 

 CELLS (BARKER, AFTER MANN). 



Two motor cells from lumbar cord of clog Danishes from the cytoplasm, 

 wi in cnViiimn+o ~~j *: i -_..-.LL A .i_ -, 1 hen follows what is perhaps 



fixed in sublimate and stained \\ith toluidin 

 blue, a, from rested dog ; i, pale nucleus ; 

 2, dark Nissl spindles ; 3, bundles of nerve 

 fibrils, b, from the fatigued dog ; 4, dark 

 shrivelled nucleus ; 5, pale spindles. 



a ' last effort ' on the part of 

 the nucleus to supply the 

 cytoplasm, in the form of a 

 discharge of chromatic sub- 

 stance, which first masses 



itself around the outside of the nuclear membrane, and thence 

 gradually diffuses into the cytoplasm. With the using up of 

 this supply all the basic chromatic material of the cell, except that 

 in the karyosome (nucleolus), is exhausted. Finally, this too is 

 yielded up to the cytoplasm, and with its consumption there 

 remains a totally exhausted cell, devoid of basic chromatin and 

 incapable of recuperation. 



According to Pugnet, even in extreme fatigue, as when dogs 

 were caused to run forty to nearly sixty miles in a special apparatus, 

 the changes varied greatly in degree in different cortical cells, from 



