DEGENERATION AND REGENERATION OF NERVE FIBERS 531 
But in this case the plexus, composed in its distal part of fairly 
parallel fibers, is directly connected with the distal stump into 
which the bundles run in great numbers. 
While of course it is not possible to follow individual fibers 
out of the central stump through the scar and into the distal 
stump, yet by a study of serial sections of different stages, it 
is possible to convince oneself that all the nerve fibers in the 
scar are outgrowths of central axons. 
3. The utilization of the protoplasmic bands as pathways for the 
new axons in the distal stump 
We have already described in the distal stump the multipli- 
cation of the nuclei of the neurilemma, the increase of the pro- 
toplasm which surrounds them, and the formation from these of 
nucleated protoplasmic bands. These bands are formed as the 
final stages in the degeneration of both medullated and non-medul- 
lated fibers. In none of the specimens was it possible to see any 
indications of the development of axonsin situ. Occasionally one 
sees in them a pseudo-striation due to longitudinal rows of gran- 
ules, but there are no transition stages between these and the 
sharply stained, regenerated axons. Negative results of this 
sort, obtained from preparations which sharply differentiate 
the finest branch of an axon, are in themselves of great signifi- 
cance. But even more important is the evidence of the direct 
growth into these protoplasmic bands of the fine nerve fibers 
of the scar. 
In Dog v, killed fourteen days after the operation, and Dog 
vi, killed nineteen days after the operation, in both of which 
the cut ends of the nerve were united by sutures, nerve fibers 
had entered the distal stump from the scar. In the nineteen- 
day specimen they can be seen to run into the protoplasmic 
bands; but in the fourteen-day specimen these bands are not 
sufficiently well developed to permit one to say whether the 
new axons have entered these developing bands or not. In 
Dog x, killed twenty-five days after excision of 1 cm. of the 
nerve, the band fibers are well developed and clearly differ- 
entiated, but there is no trace of a new axon in the sear covering 
