Ranson, Degeneration in Spinal Nerves. 285 



difference, howeve amounts to only 15 per cent, of the smaller 

 number, and this can readily be accounted for in terms of normal 

 growth. There seems, therefore, to be little if any tendency to 

 repair the ventral roots in the sense of an acceleration of the nor- 

 mal rate of fiber formation to compensate for a previous loss. Of 

 course the neurones represented by the degenerating fibers in the 

 root undergo complete destruction (p. 270) and no regeneration 

 of the injured axons could be expected. But it was deemed possi- 

 ble that some reserve cells might be located in the ventral cornua, 

 which might take part in a reformation of the ventral root after 

 the neurones whose axons originally entered into its formation had 

 been destroyed. There is no evidence that such a compensatory 

 process occurred in this set of experiments; and if reserve cells are 

 present in the ventral cornua of the spinal cord, they certainly failed 

 to respond to the demands placed upon them by the conditions of 

 this experiment. 



The excess of fibers in the dorsal roots four months after the 

 operation, as compared with those at the two-month period, 

 amounts to less than i per cent. This is less than would be ex- 

 pected on the basis of normal growth processes, and it is certain 

 that during the second two of the four months intervening between 

 the operation and the autopsy there was no tendency for the small 

 latent cells to increase their normal rate of development in an 

 attempt to restore the atrophied dorsal roots to their normal con- 

 dition. 



The fact that both the ventral and dorsal roots show more fibers 

 four months after the operation than at an earlier period, indicates 

 very clearly that there can be no slow progressive degeneration 

 going on in these localities. This fact is of interest, since retro- 

 grade degeneration has usually been regarded as a chronic pro- 

 gressive process. In this case it ran a rather rapid course and 

 came to a definite termination. 



III. Significance of Differences in the Ages of the Animals. 



It has been shown what the effects of cutting the second cer- 

 vical nerve are in the young rat and what influence is exerted by 

 the lapse of a greater or less length of time between the operation 

 and the autopsy. It is now our purpose to inquire how far these 

 results are dependent upon the immaturity of the animal used for 



