DEGENERATION AND REGENERATION OF NERVE FIBERS 527 
In the case of the non-medullated axons, which after an abor- 
tive regeneration undergo a cellulipetal degeneration for some- 
thing more than one centimeter up the proximal stump, true 
regeneration begins about the fourteenth day. There occurs 
a downgrowth of new axons from above the point where the 
degeneration ceased. ‘These new axons, on the growing ends 
of which small bulbs can be seen, grow toward the cut surface 
in the degenerated bundles. These new axons continue to 
increase in number until by the thirty-fourth day the bundles 
of non-medullated fibers in the last part of the proximal stump 
are larger and more compact than in a normal nerve. Although, 
because of the smallness of these fibers and the compactness 
with which they are grouped, it is not possible to demonstrate 
the occurrence of lateral branches on these fibers, there can 
be no doubt but that they have increased greatly in number. 
This is evident in the longitudinal sections, but even more so 
in transverse sections taken a short distance above the lesion 
(fig. 26, a). Here one sees large bundles of non-medullated 
fibers so closely grouped as to resemble a sympathetic nerve. 
Compare this drawing with figure 25 taken at a lower level and 
showing the multiplication of the branches of the medullated 
fibers. It will be seen that the medullated fibers in the neigh- 
borhood of the non-medullated bundles in figure 26 have not 
yet begun to give off branches. Hence the large increase in 
the non-medullated fibers cannot be due to the side branches 
of the medullated fibers growing into the bundles of non-medul- 
lated fibers. These bundles can be traced to the end of the 
central: stump, where they go over into the scar intermingling 
with the branches of the medullated fibers from which they can 
no longer be distinguished. 
This enormous increase in the number of fibers in the termi- 
nal part of the proximal stump is one of the most striking obser- 
vations that have been made on these preparations—and it seems 
to the writer one of the most significant for the interpretation 
of the nature of the regenerative process. It fits logically into 
the scheme of the outgrowth theory. As we shall see, a great 
number of fibers fail to find their way through the sear to the 
