nae S. WALTER RANSON 
more sharply differentiated than in normal axons. Some of 
these fibrils detach themselves from the axon at its surface 
to form fine branches, which run in various directions on the 
surface of the axon and after a short course end in small bulbs 
(fig. 17). Some of these branches, which arise near the cut 
surface find their way out into the exudate, but most of them 
continue to grow within the old sheath. In the absence of the 
myelin sheath, which is entirely disintegrated in these last few 
tenths of a millimeter of the proximal stump, these branches 
reach the neurilemma and immediately underneath this they 
continue to grow in a circular or spiral direction, interlacing 
with one another. In this way there develops by the third or 
fourth day, just beneath the neurilemma, a hollow cylinder 
formed by fine interlacing fibers, within which the old axon can 
be seen (fig. 18, a, b). Many of these fine fibers can be seen 
ending in little rings. While the majority of them remain 
within the old neurilemma sheath, a few, leaving it at the cut 
surface, run into the exudate and a few others, piercing the 
sheath, run into the eudoneurium. 
‘In figure 19 the axon is seen giving off some relatively coarse 
branches, some of which have arranged themselves in a tubular 
sheath. The axon and part of the sheath are cut away in one 
place, where they run out of the section. 
In some of the medullated axons the fibrillar dissociation 
represented in figure 15 and the branching illustrated in figure 
17 seem to be associated in the production of a tubular network. 
Sometimes the central axon can be seen to break up into this 
network and be reformed from it again at a lower level. 
The formation of a zone of reaction, the fibrillar dissociation, 
and the formation of the early collateral branches within the 
old neurilemma sheath, together with the tubular networks 
which have just been described, constitute the early changes 
in the medullated axons which were first seen by Perroncito 
and which Cajal has called Perroncito-phenomena. On _ the 
eighth, fourteenth and nineteenth days all of these structures 
become less and less evident, and their place is taken by paral- 
lel coursing fibers, of which there are a large number within 
