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

58 INJURIES OF NERVES.
visible vessels then abruptly enlarge, new ones come into
view, and the part obviously darkens.*
Precisely the same etiects follow when we freeze a nerve,
and this is the case whether we protect its tissue from the
chemical influence of the rhigolene or act upon it directly.
I have usually preferred to cover it with thin rubber, or
with a layer of some neighboring tissue. In some instances
the nerves were frozen once, and examined after
half an hour. In others the freezing was repeated once
or several times, at intervals of hours or days.
When a single brief freezing has been effected, there is
usually a distinct congestion, which very soon lessens, and
at all events leaves behind it no changes which can be
seen under the lens. In more prolonged freezings, or
when these had been repeatedly employed, distinct lesions
were visible, and even to the unassisted eye the nerve
looked darker, and in some cases larger, than was natural.
Sections of nerves in this condition exhibit a seeming increase
in the number of vessels, as well as frequent vascular
ruptures, which dot the nerve with interfibrillar
clots ;
while in some cases, long lines of red mark where
the escaping blood has followed the areolar interspaces
between the grosser divisions of the nerve. Cases as
grave as this are not merely congestions, but actually apoplexies
of the neural tissue, and show their influence in
the animal used, by lameness, and sometimes by distinct
lessening of sensation in the parts to which the congested
nerve is related. Of course the minor symptoms of sensory
disturbance are incapable of study in the animal.
* In the spine, as in the nerve trunks, sudden loss of power
is the
primary result of freezing, then follows a rapidly-increasing congestion,
which is marked, in the case of the spinal cord in birds, by certain epileptiform
phenomena of a very instructive character.
See Am. Journ Med. Sci., Jan. 1867, and Jan. 1868, for my own researches
on this subject.