DEGENERATION AND REGENERATION OF NERVE FIBERS 519 
The interpretation which is to be placed on these okserva- 
tions is as follows: The non-medullated fibers degenerate a 
short distance (about 2 em.) in a central direction and the 
degenerated portions undergo the changes looking toward the 
formation of protoplasmic bands. But before these are fully 
formed the cellulipetal degeneration has been arrested and 
regeneration begins. The fibers above the point where the 
degeneration ceases begin to grow downward and on their ends 
bulbed extremities can be seen. The great increase in the 
number of these fibers in the proximal stump near the lesion 
indicates that there also are formed lateral branches, although 
on account of the compactness of the bundles it has not been 
possible to observe the branching directly. Cajal describes 
and figures the branching of non-medullated fibers in the proxi- 
mal stump, but it seems probable that he was dealing, not with 
the original non-medullated fibers but with new axons, which 
had branched off from the medullated fibers (fig. 22). The 
new non-medullated axons follow the old fiber bundles as path- 
ways and at the cut end of the nerve they finally reach the scar, 
into which they run. 
2. Early changes in the medullated axons of the proximal stump 
a. Formation of a zone of reaction. In the immediate neigh- 
borhood of the lesion one sees changes in some medullated axons 
that greatly resemble those seen at an early stage in the distal 
stump. Figure 14 represents a typical fiber of this sort at the 
end of the first day. At d one sees the axon staining like the 
normal axon a light yellow; but it is beginning to increase in 
diameter. As we follow it from the central (c) toward the 
peripheral end (p) it increases in size and assumes a darker 
stain. At the same time, indications of a neurofibrillar reticu- 
lum make their appearance. At 6 the axon is several times 
its normal thickness, filling and distending the neurilemma. 
It shows at this point, and for a short distance ‘above, a dense 
deeply staining reticulum. This corresponds to the club-like 
zone of reaction seen in figure 10, except that the neurofibrillar 
reticulum is more pronounced. At a the disintegrated remains 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 6 
