68 THE AMERICAN MONTHLY (Mar 
(1) Degeneration of nerve-fibers, axis cylinders, and 
myelin sheaths.—The axis cylinders become vacuolated, 
soon break up, and, as described by Von Bungerand others, 
many fragments of axis cylinder may be seen enclosed in 
myelin balls inside the neurilemma sheath. The myelin 
breaks up into smaller and smaller balls and eventually 
disappears. These changes are better marked near the 
periphery of the affected nerves; but they do not gradu- 
ally become more advanced the further the nerve is traced 
from it origin. Healthier portions of a nerve fiber may 
be seen between more degenerated parts, and careful study 
of many sections cut from a single nerve, such as the an- 
terior tibial, demonstrates one remarkable point to which 
far too little attention has been directed, namely, that the 
segmental nuclei—i.e., the nucleiof the neurilemma sheath, 
have a very important trophic influence over the axis 
cylinder which it protects; it has been fairly definitely 
demonstrated that these segmental nuclei proliferate rap- 
idly once the axis cylinder and myelin sheath have de- 
generated ; but it is important to note that in these inter- 
vening more healthy parts of a nerve fibre, the integrity 
of the segmental nucleus and the integrity of the axis cy]- 
inder occur together. 
It has even been suggested that the new axis cylinders 
may develope from segmental nuclei in the processes of 
regeneration of a nerve fibre. But, although this is con- 
trary to my experience, and from an embryonic stand- 
point is most improbable, such statements show that to 
these segmental] nuclei more important functions are de- 
scribed than formerly, and indirectly they strengthen the 
position which I take up. 
The disintegration of the myelin sheaths requires no 
special description, as it is exactly similar to the degen- 
erative changes which occur in a nerve fibre undergoing 
degeneration after section from its trophic cell. 
I wish, however, to draw your attention to the fine med- 
