Ranson, Degeneration in Spinal Nerves. 



287 



all the peripheral fibers ever to develop are present in the nerve, 

 some as medullated, the rest as non-medullated fibers; and this 

 if it should be found to be the case, would help to explain the fact 

 that the reaction is the same in the adult as in the young animals. 

 Table XI gives only the average number of cells present in the 

 ganglia under each of the three conditions; Table XII shows that 

 the agreement which was found between the averages is just as 

 apparent when all the individual ganglia are brought together. 

 It does not matter whether the animal is young or old or whether 

 it survives for two or for four months; the changes in the spinal 

 ganglion are always the same. 



TABLE XII. 



Showing the Uniformity in the Cell Destruction in the Spinal Ganglion Resulting 

 from the Section of the Peripheral Nerve. 



By reference to Table XI it will be seen that the number of ven- 

 tral root fibers is nearly the same in both sets of rats that survived 

 four months, whether the operation was made when they were 

 12 or 120 days old. This indicates that the same number of ven- 

 tral root fibers dropped out in each case, after which the nerve 

 fibers continued to develop at the normal rate in the immature 

 animal. Hence, since the number of medullated fibers was 

 smaller in the young rat, those that degenerated must have con- 

 stituted a larger proportion of the entire number than in the case 

 of the adult rat. And this is in accord with the general belief that 

 immature neurones succumb more readily to an axonal lesion than 

 do the fully developed ones. This variation in reaction, according 

 to the age of the animal, is very pronounced in the case of the fibers 

 of the corpus callosum (Ranson '04). In a rat twelve hours old 

 in which the corpus callosum was injured, the injured fibers under- 

 went complete degeneration, both Wallerian and retrograde; 

 in a rat of three months the retrograde degeneration affected only 

 the part of the fiber in the immediate vicinity of the lesion. 



