THE NERVOUS SYSTEM. 803 



when separated from their cell bodies. Thus in the divided peripheral 

 nerve those fibres which are the processes of the spinal ganglion cells 

 undergo the same degenerative changes as do the fibres which are proc- 

 esses of cells of the anterior horn. Most dendritic processes are, how- 

 ever, so short and terminate in the gray matter so near the cells from 

 which they originate that experimental separation of the process from 

 its cell body is impracticable. In view of the fate of the axone, however, 

 and the relation of the dendrites to the cell body, there can be little 

 doubt that as complete degeneration follows the severance of a proto- 

 plasmic process from its cell of origin as follows in the case of the axone. 



(c) CHANGES IN THE PROXIMAL STUMP AND IN THE CELL BODY 

 RESULTING FROM LESION TO THE AXONE. The fundamental principle 

 of the law of Waller was the complete degeneration of the distal portion 

 of the divided nerve, while the proximal stump remained intact. Our 

 present conceptions, however, of the interdependence of the different 

 parts of the neurone, and of the axone as the outlet for neurone energy, 

 would lead us to expect certain changes of an atrophic nature in the 

 proximal stump and in the cell body, as a result of separation from its 

 axone and consequent inability to functionate. That such changes take 

 place recent improvements in cytological technique have enabled us 

 to determine. The method of Marchi shows that degenerative changes 

 occur not only in the distal, but in the proximal end of the divided 

 nerve. These changes take place more slowly than in the distal portion 

 but are apparently identical in character. 



In the body of the cell the method of Mssl demonstrates marked 

 changes after section of the axone. These changes may be observed 

 within twenty-four hours after the injury. They consist in a diminu- 

 tion in the chromatic elements of the cell, chroinatolysis. This is most 

 marked in the central portion (central chromatolysis), a distinct ring 

 of chromophilic bodies around the periphery often remaining. The 

 nucleus usually migrates toward the periphery and may even bulge 

 from the cell. In the case of the hypoglossal nerve in the rabbit, these 

 changes reach their maximum in from two to three weeks. The future 

 of some of these cells is complete degeneration. Others apparently un- 

 dergo regeneration. The intensity of the reaction of the nerve cell to 

 injury to its axoue depends upon the severity of the injury. Thus cut- 

 ting the nerve is followed by more prompt and marked changes in the 

 nerve cell than simple compression, while pulling out the nerve roots is 

 followed by a still more intense reaction. Again, there is a difference in 

 the resisting-powers of different types of cells. Thus the motor cells of 

 the anterior horn are peculiarly resistant to injury to their axones, as 

 are also the spinal ganglion cells to injury to their central processes. 

 Again, between cells of the same type there are marked variations in re- 

 sisting-powers. Thus the motor cells of the anterior horn are much more 

 resistant than the cells of the motor cranial nuclei. ' 



1 For review and bibliography of changes in the nerve cell and in the proximal stump 

 after section of a peripheral nerve consult Barker, "The Nervous System," p. 229 et seq. 



