DEGENERATION AND REGENERATION OF NERVE FIBERS. 515 
eration of these fibers in the distal stump. In the last 0.8 mm. 
of the proximal stump one sees at the end of twenty-four hours 
the formation of lateral branches on the non-medullated fibers. 
The stages in the formation of these branches are illustrated in 
figure 12. The earliest stage is seen at d, and consists in the 
development on one side of the fiber of a spherical mass several 
times thicker than the fiber and staining only a trifle less intensely 
than the fiber itself. These masses seem to possess the power of 
ameboid movement and work their way out of the fiber bundle in 
which they orignated, pulling on the fiber and forming a V-shaped 
bend in it. Three stages of this are seen at d, c and e. As 
the mass moves farther it comes to be connected with the V- 
shaped bend in the old fiber by a single limb which is formed 
behind the mass as it moves forward. Thus the V becomes 
transformed into a Y (fig. 12, 6). As the lateral branch is formed 
it often happens that the distal limb of the V degenerates. The 
distal limb of the V in ¢ can be followed only a short distance 
when it goes over into a finely granular thread (not shown in 
the drawing) and disappears. The fiber and bulb seen at a 
are to be accounted for in this way. The bulb appears as if on 
the end of a fiber which has turned at right angles and left the 
bundle. 
The composition of the bulbs on the ends of the lateral branches 
varies. At first (fig. 12, c, d, e) the neurofibrillar content is 
fine and uniformly distributed, giving to the bulb a stain almost 
as dark as that of the fiber. At this stage the fibrillar plexus 
can only rarely be seen. As growth continues the interfibrillar 
substance increases greatly in quantity and out of proportion 
to the increase in fibrillar substance. This may, in rare cases, 
lead to the formation of a wide meshed neurofibrillar reticulum 
(fig. 12, 6) or more often to the accumulation of a large mass 
of lightly staining substance about a central fibrillar core. This 
central core is about the size of the original bud from the side 
of the fiber. 
It should be noted that the bulb shown at 6 is an exceptional 
one in the clearness with which the fibrillar reticulum is stained 
and in the fact that it gives off secondary branches. There 
