80 S. WALTER R ANSON 



sal root fibers have their cells of origin in the spinal ganglion this 

 last statement seems incredible. 



These observations are, however, easily explained on the basis 

 of the facts already presented. The excess of the number of 

 cells destroyed over the number of medullated axons cut in the 

 division of the nerve is explained by the presence of the non- 

 medullated axons. And the fact that the majority of the medul- 

 lated fibers of the dorsal root remained intact after the loss of 

 more than half of the spinal ganglion cells is explained bj^ the fact 

 that the cells which disappear are chieflj^ small cells whose axons 

 both in their central and peripheral prolongations are non- 

 meduUated 



In concluson it may be said that there are in the spinal nerves 

 a very large number of non-medullated nerve fibers. They are 

 in fact more numerous than those which are medullated. While 

 a few are no doubt derived from the sympathetic system by way 

 of the gray rami communicantes, the experimental and numerical 

 evidence just presented makes it clear that at least a great many 

 of them are the peripheral branches of the axons of the small 

 cells of the spinal ganglia. We now have a satisfactory expla- 

 nation for the excess of spinal ganglion cells over medullated 

 afferent fibers and for the chromatolysis which appears in practi- 

 cally all the cells of a spinal ganglion after its associated nerve 

 has been divided. 



It is obvious that this investigation raises more questions 

 than it settles. We have yet to determine the central course of 

 these axons, whether any pass by the ventral root, and what 

 proportion come by way of the rami communicantes. It will 

 also be necessary to determine whether they are distributed 

 chiefly to the skin muscles or blood vessels. If they go chiefly 

 to the skin it may be possible that they are associated 

 with some one or more of the varieties of cutaneous sensation. 

 It will be necessary also to repeat the Wallerian experiment and 

 study the degeneration of these fibers. In the pathology of the 

 peripheral nerves it will be of interest to learn how these fibers 

 behave in tabes dosalis, neuromuscular atrophy and other con- 

 ditions in which the pathology, so far as it relates to the peri- 

 pheral nervous system is very obscure. 



