570 



SIGNIFICANCE OF THE NERVOUS SYSTEM 



changes belong in the same category as those following the separa- 

 tion of the cell-bodies- from their axons, when the central stump and 

 adjoining cell-bodies undergo retrogressive degenerative alterations. 

 We then obtain a turgescence of the cells which is superseded by 

 atrophic changes and chromatolysis. 



The fact that the gray substance of the centers has a dej&nite meta- 

 bolic requirement, is also shown by the grave symptoms which follow 

 almost immediately upon the occlusion of the carotid arteries or upon 

 obstructions to arteries which supply individual centers of the cere- 

 brum. A functional uselessness of those ganglion cells then results 

 which are situated distally to the block. This uselessness is evinced 



either by a loss of motion or sensa- 

 tion, or both. A similar condition 

 / 1 1 \ ' J \ may be set up very quickly in rabbits 



iIrA ' c\ by compressing the abdominal aorta 



^ •^ '' ^ (Stenson's experiment). The anemia 



of the spinal centers resulting from 

 this obstruction, soon leads to a pa- 

 ralysis of the posterior extremities and, 

 peculiarly enough, the motor paraly- 

 sis precedes the loss of sensation (anes- 

 thesia). This dissociation suggests a 

 difference in the resistance of different 

 nervous elements to anemia. 



Verworn^ states that the fatigue 

 of nerve cells may be brought about 

 in two ways, namely, by causing an 

 accumulation of the waste-products or 

 by exhausting the reserve nutritive 

 material of the cell. The former in- 

 duces fatigue and the latter, the more 

 serious condition of exhaustion. The 

 experiments which are directly con- 

 cerned with the metabolism of nerve 

 centers, consisted in perfusing the 

 central nervous system through the aorta with defibrinated blood and 

 saline solution containing varying amounts of oxygen. Thus, if the 

 blood of a frog poisoned with strychnin, was slowly displaced by saline 

 solution free from oxygen, the muscular spasms gradually became less 

 violent and finally disappeared altogether. The subsequent perfusion 

 with thoroughly aerated defibrinated blood, however, soon caused 

 these spasms to reappear with renewed intensity. The same results 

 were obtained with saline solution fully charged with oxygen, while 

 blood serum free from oxygen, prevented the recurrence of the spasms. 

 This observation proves very conclusively that the recuperation is not 

 dependent upon the organic substances, but rather upon the oxygen; 

 1 Arch, ftir Anat. und Physiol., 1900, 385. 



Fig. 284. — Two Motor Cells 

 FROM THE Lumbar Cord of a Dog. 



A, From rested, and B, from 

 fatigued dog; showing the diminu- 

 tion in the size of the cell, the changes 

 in the size and shape of the nucleus 

 and the chromatolysis. (After 

 Mann.) 



