75 6 A MANUAL OF PHYSIOLOGY 



nucleus shrinks ; the nucleolus is obscured or may disappear alto- 

 gether. At the same time the processes of the cell, and especially 

 the dendrites, tend to atrophy (Fig. 310). 



Nutrition of the Neuron. We have already seen that when an 

 axon is cut off from its cell-body, it and its medullary sheath, when 

 it possesses one, undergo a rapid degeneration. It was long sup- 

 posed that no change took place in the nerve-cell. The researches 

 of recent years have shown that not only does loss of the specific 

 function and trophic influence of the cell-body affect the nutrition 

 of the axon, but loss of function of the axon reacts on the cell- 

 body. In many cases at least, when a nerve-fibre is divided from 

 its cell characteristic changes are produced in the latter and in 

 its dendritic processes, and they are scarcely less rapid, although 

 usually less profound, and far more transient than the degeneration 

 in the peripheral portion of the nerve-fibre. The cell-body and the 



FIG. 311. CELLS FROM THE NUCLEI OF THE OCULO-MOTOR NERVES OF THE CAT 

 THIRTEEN DAYS AFTER DIVISION OF THE ROOT-FIBRES ON ONE SIDE : 

 NISSL'S STAIN (BARKER, AFTER FLATAU). 



a, normal cell from side on which the roots were not cut ; b, cell from side 

 operated upon. Only a few Nissl bodies are present in b, and the nucleus is 

 displaced to one side of the cell. 



nucleus swell. Many of the Nissl bodies (Fig. 311) disintegrate, and 

 are reduced to a finely granular condition. After a time much of 

 the disintegrated chromatic substance disappears altogether. The 

 nucleus may be displaced to one side of the cell. Certain changes 

 in the neurofibrils of the cell may accompany the changes in the 

 chromatin. In rabbits after division of the facial nerve the 

 alterations in its nucleus of origin have been found to reach a maxi- 

 mum in about three weeks, after which there is a tendency to recovery 

 on the part of the majority of the cells, even when regeneration of the 

 nerve has been prevented by cutting out a portion of it. Some of 

 the cells may completely atrophy and disappear. Similar changes 

 have been found by Warrington in the motor cells of the anterior 

 horn after section of the posterior (dorsal) spinal roots. Since in 

 this case no anatomical injury has been inflicted on the motor 



