Dunn, Medullated Nerve Fibers. 697 



sponding segments of the legs of the two frogs. On comparing mus- 

 cular branches we find that the right thigh of frog E, Table IV, 

 has 1597 medullated nerve fibers as against 1830 in the right thigh 

 of frog IIB, an excess for frog IIB of 237 medullated nerve fibers, 

 or 13 per cent of the fibers in the muscular branches of the right 

 thigh of frog IIB. The cutaneous branches for the right thighs 

 show 1553 medullated nerve fibers for frog E as against 1678 medul- 

 lated nerve fibers for frog IIB, an excess for frog IIB of only 125 

 nerve fibers, or 7 per cent of the nerve fibers in the cutaneous 

 branches of the right thigh of frog IIB. In the right shanks the 

 excess for frog IIB is, among the muscular branches, 341 nerve 

 fibers, and among the cutaneous branches 100 nerve fibers. In each 

 segment of the right leg the operated frog E shows a greater varia- 

 tion from frog IIB in the number of nerve fibers within its muscular 

 branches than in the number of nerve fibers within its cutaneous 

 branches. This again may be a matter of individual variation or 

 may show a loss of medullated nerve fibers from the muscular 

 branches of the right leg of frog E. If the latter is the condition, 

 the inference naturally follows that the difference is due to a loss 

 of nerve fibers during the long period of artificial inactivity, and 

 that the degenerated fibers may be efferent in character. Several 

 unsuccessful attempts have been made to test this possibility in con- 

 trol frogs kept in similar conditions, but as no decisive findings can 

 be quoted at the present time it seems best not to delay the publica- 

 tion of the present paper for a longer time, in order to secure such 

 findings. 



It seems, however, advisable to consider the arguments for and 

 against efferent degeneration in the right leg of frog E, even though 

 the percentage of such possible degenerating medullated nerve fibers 

 is small, being about 1 per cent for the thigh. Of interest in this 

 connection are the findings for the branches to the thigh in two 

 frogs of the same length and of approximately the same weight, 

 Dunn, 1900, pages 233 and 234. With a weight difference of but 

 4.3 grams, the heavier frog B had 212 more muscular nerve fibers 

 in the right thigh than had frog C, but a less number of cutaneous 

 medullated nen^e fibers by 403 than had frog C. These numbers 

 certainly argue for a wide range of individual variation. 



