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

76 INJURIES OF NERVES.
as the sixth day. At all events, this change corresponds
with the partial loss of excitahility in animals. In man,
the earliest total loss of power to respond to electricity
which I have seen was on the seventh day. At or about
this time the whole substance of Schwann begins, in
birds, to undergo irregular segmentation, a process which
is slower in dogs and rabbits. The double contour
of the fibres becomes irregular at as first, though the
myoline were indented more or less deeply. Then the
segmentation grows more complete, and the outlines of
the fibres more broken, so that the myoline is finally to
be seen distributed along
the sheath of Schwann in
masses, which are round or elongated and irregular at
first, but which, by the third to the sixth week, become
smaller, more numerous, and rounder, so that, in most
cases, at the close of three months, the nerve tube holds
only the finest granular elements. More or less speedily
this remnant of the white substance of Schwann disappears,
and the sheath of Schwann becomes shrunken,
and, as it were, wrinkled, the whole nerve being now
distinctly of a dull gray tint, and looking like a firm
bundle of connective tissue.
When the nerve has reached this final condition of
degeneration, there are still present in the sheath here
and there a few minute molecules of fatty matter, and
occasionally such masses are also observed lying between
the fibres. Laverran has noted at this period, within the
sheath, certain minute collections of matter very slightly
retractile, and which I have also noticed, though not constantly.
They resemble, optically, colloid substance, or
portions of escaped myoline. After this time, there does
not seem to be any notable change in the residual sheath,
except, perhaps, a slight shrinking, and in some cases an
increase in the amount of interfibrillar fatty molecules.
The alteration of the white matter of Schwann has been