Injuries of nerves and their consequences - Reflex Sympathetic ...

PATHOLOGY OF NERVE LESIONS. 77
described as fatty degeneration
; but, as Eobin has remarked,
it is largely fatty in the iirst place, and the
alteration may consist only in its being broken np and
removed, there being no evidence that any such substitution
has taken place, as is found to occur in ordinary
instances of fatty degeneration.
The utmost difference of opinion exists as to the persistence
of the cylinder axis during these progressive
transformations of the nerve. The majority of observers
incline towards belief in its
permanence, and so far as my
own researches are concerned, I am also of this opinion,
although regarding it as a point most difficult of decisive
settlement.*
The degeneration has been described as passing from
the centre to the periphery, but I am satisfied that it
affects at one and the same time the whole length of the
nerve. For although
it is true that a current which, at
the sixth day after section may not cause motion, when
applied at the upper limit of the nerve, ma}^ still do so
when used nearer to the muscles, this is due to the fact
that in the former case it has to overcome the resistance
offered by a longer track of altered nerve.
If we ask ourselves why the nerve alters after division,
several answers seem possible.
The nerve may change
because its function is abolished,— the central part of a
motor nerve failing to alter owing to its being traversed by
* The rate at which the nerve change occurs varies greatlj- in different
animals, being rapid in birds, and slower in the rodents. In the frog it
is most speedy in hot weather, and in the hibernating animals Schiff
states that it is so singularly slow, that five weeks elapsed in the marmot
with less change than five days produced in the dog. In the snapper,
Clielonura seiyentina, I found it to be equally tardy during the winter.
Some j^ears ago, in the autumn, I cut the left sciatic nerve in two box
turtles, which soon buried themselves in my garden. On their reappearance
in April, I found the nerves quite unchanged. Within the next
month the peripheral end of the nerve underwent complete alteration.