2O2 



NERVE-CENTRES. 



[CH. XVII. 



remain unaffected. If regeneration of the fibre, and restoration 

 of function takes place, no change is observable. But if regenera- 

 tion does not occur (and it does take place in the central nervous 

 system), the cell and its processes undergo a slow chronic wasting ; 

 one of the earliest signs of this disuse atrophy is chromatolysis. 

 Warrington has recently shown a still more interesting fact, 

 namely, that section of the posterior roots causes chromatolysis 

 in the anterior horn cells of the same side ; this indicates that 

 the loss of sensory stimuli produces a depression of the activity 



Fig 206. Nissl's granules. A. Normal pyramidal cell of human cerebral cortex. B. Swollen 

 cedematous pyramidal cell from a case of status epilepticus. Notice diffuse staining, and 

 absence of Nissl's granules ; the nucleus is enlarged and eccentric. The lymph space 

 around the cell is dilated. C. Pyramidal cell of dog after ligature of vessels going to 

 brain and consequent ansemia. Notice great swelling of the nucleus, and advanced 

 chromatolysis, most marked at the periphery of the cell. 



and metabolic functions of the spinal motor cells. We shall see 

 later on that this accords quite well with the physiological effects 

 observed under these conditions. 



The accompanying figures show the normal appearances pre- 

 sented by nerve-cells when stained with methylene blue, and the 

 abnormal conditions observed in some of the pathological states 

 alluded to in the preceding paragraphs. The letterpress beneath 

 the figui-e should be carefully consulted. These drawings are 

 made from photo-micrographs kindly lent me by Dr. Mott. The 

 magnification in all cases is 700 diameters. 



