488 S. WALTER RANSON 
these nerves are stained by a modification of Cajal’s method, 
which we have called the pyridine-silver method, very many 
fine nerve fibers are seen in the endoneurium between the medul- 
lated fibers (Ranson ’11). These are stained black with reduced 
silver and are devoid of a myelin sheath, while the medullated 
axons are light yellow and are surrounded by a colorless sheath 
of myelin. The non-medullated fibers may run singly but are 
usually grouped into small bundles. Although no attempt 
has been made to determine their exact number, it is easy to 
see that they far outnumber those which are medullated. On 
tracing these fibers back toward the spinal cord, it is found that, 
while a certain number can be seen entering the nerve via the 
gray ramus communicans (Chase, unpublished observations), 
the vast majority of them enter the nerve by way of the dorsal 
root. A study of the spinal ganglion (Ranson 712) has shown 
that these fibers are derived from the axons of the small cells 
of the ganglion by a T- or Y-shaped branching. Because of 
the location of the cells of origin in the spinal ganglion, and 
because of the characteristic 7- or Y-shaped branching of the 
axons there need be no hesitancy in regarding them as afferent 
and not sympathetic in function. 
As has been intimated, it was our purpose, when the series 
of experiments to be reported in this paper was begun, to cut 
first the peripheral nerve and then, in other experiments, the 
roots proximal to the spinal ganglion in order to determine the 
direction of degeneration of these fibers. The division of the 
sciatic nerve of the dog was undertaken to exclude by the direc- 
tion of degeneration the possibility that some of the non- 
medullated fibers might arise from cells located at the periphery 
(a common location of such cells in invertebrates). In another 
series of experiments the roots, proximal to the ganglion of the 
second cervical nerve of the dog, were cut to determine whether 
any non-medullated fibers arose from cells located in the gray 
substance of the spinal cord. Since the results of these two 
series of experiments were complicated by a variety of regenera- 
tive changes in the nerve, ganglion and roots, it has seemed best 
to present the two series of experiments in separate papers. 
