BERRY— HINSEY: RECOVERY, REGENERATING NERVES 571 



duction velocity. Holmes and Young^ have described this phenomenon 

 and have shown that the connective tissue tubes in the distal stump 

 undergo shrinkage during the delay period. The experiments reported 

 here show that delay causes even greater influence than they descril)ed. 

 This difference in results is probably due to the fact that our experi- 

 ments allowed the nerves to regenerate for much longer periods, during 

 which the restrictive influences could be more strongly exerted. How- 

 ever, the results show that brief delay periods have little effect, but that 

 delays of 253 and 476 days produced considerable interference with 

 fiber reconstitution. Unfortunately, the exact delay times between 

 no effect and slight effect could not be determined from these experi- 

 ments. The introduction of control cross-sutures, without delay in 

 nerves of the opposite leg of the same animals, seems to rule out the 

 factors operating at the suture line, or differences in peripheral re-in- 

 nervation (unless atrophy of the muscle is considered), which can in- 

 fluence the fiber reconstitution. Presumably, therefore, only differ- 

 ences in the condition of the connective tissue and Schwann tubes of 

 the distal stump are responsible for the results in these experiments. 



The influence of the connective tissue or Schwann tubes in the distal 

 stump on the fiber growth has been recently emphasized by Sanders and 

 Young,^ who found that the motor branches of a sutured, mixed nerve 

 contained fibers of larger caliber than the sensory branches. Also, 

 Simpson and Young'* cross-sutured somatic nerves into the splanchnic 

 and anterior mesenteric nerves and suggested that the restriction in 

 fiber diameter which resulted might be due, in part, to the small size 

 of the peripheral tubes. The results reported here by Hammond and 

 Hinsey'' showed this same restriction in cross-sutures of the hypoglossal 

 and cervical sympathetic. However, in these experiments, the nerves 

 were allowed to regenerate for longer periods than reported by Simpson 

 and Young,^ and an additional phenomenon was disclosed. At 216 

 days after cross-suture of the hypoglossal to the cervical sympathetic, 

 the recovery of fiber diameter was slightly less than that obtained in 

 control, hypoglossal-to-hypoglossal, sutures. At 250, 300, and 365 

 days, the fibers not only showed greater restriction of growth, but actu- 

 ally the caliber of the fibers found distally became smaller than they 

 were at 216 days. There is no conclusive explanation of this apparent 

 reversal of diameter growth, but two facts might be mentioned. First, 

 the final histogram (figure 7), at 365 days, resembled that of the orig- 

 inal distal stump before operation, and, perhaps, the small tubes com- 

 pressed or killed off the larger fibers. Secondly, it must be recognized 

 that the hypoglossal fibers could not reach proper end organs by grow- 



