a? S. WALTER RANSON 
ing end bulbs and one small fasciculus at the periphery of the 
nerve in which many well stained side branches and bulbs are 
seen. These resistant elements correspond to the central ends 
of the resistant non-medullated fibers, which, it will be remem- 
bered, retained their staining reaction for a period of two or 
three weeks. All of these resistant fibers with the branches 
and bulbs at their central ends have entirely disappeared before 
the twenty-fifth day and no traces of them are to be found in 
the preparation taken on that day. 
Changes of the same nature occur in the medullated fibers. 
In the immediate vicinity of the lesion (0.5 mm.) many of the 
medullated axons present a zone of reaction, which separates . 
the, as yet, normally staining distal stretch, from a very short 
disintegrated piece of the axon at the cut surface. This zone 
of reaction becomes more marked on the second and third days. 
There is almost no limit to the variety of appearances which the 
reaction zone may assume; but the fiber illustrated in figure 10 
may be taken as showing the principal factors involved. The 
myelin sheath in this part of the fiber is already broken up and 
appears as granular detritus filling the old sheath. Imbedded 
in this mass we have the axon and its products. The central 
and peripheral ends of the fiber are marked ¢ and p, respec- 
tively. The proximal part of the axon has completely degen- 
erated; fragments of it can be seen at a. At 6, the axon shows 
a sharply defined club-shaped enlargement which represents 
the end of the living part of the axon. Following the axon in 
a peripheral direction, one sees at the distal end of the enlarge- 
ment a distinct neurofibrillar reticulum. Below this the axon 
contracts, expands, contracts again and goes over into a second 
wider meshed fibrillar reticulum. From both of these reticula 
fine black fibrils, d, are given off which run by themselves in 
the degenerated myelin. These isolated fibrillar branches are 
also seen on the central side of the club-shaped enlargement. 
The reaction in the medullated axons therefore consists of (1) 
the formation of a distinct line of separation between a short 
dead segment and the remaining distal stretch of the fiber, 
which is still living, (2) the appearance near this line of separa- 
