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

NEURO-PHYSIOLOGY. 53
presence and severity have been the first indications which
called attention to the arrest of local circulation by clot.
Instances of venous occlusion difier somewhat in being
less entire, and also in the increased rather than the
diminished pressure which they bring about.
Undoubtedly, the nerves are excited under these circumstances,
but the cause of their excitation does not
seem to be very clear. Brown-Sdquard attributes it to
the gradual collection of carbonic acid in the tissues; but
there are other elements of disintegration which may not
be incompetent to disturb
the nerves, and his hypothesis
has found less acceptance than might have been expected
from the really strong arguments which its author has
adduced in its favor. Vulpian, on the other hand, is disposed
to consider the absence of oxygen as more likely
to occasion these excitations,
— a view which certainly has
less to recommend it than that of the former physiologist.
Perhaps the causation may be more complicated than has
been suspected, and at all
events the sudden annihilation
of nutritive osmoses and the novel conditions of pressure
cannot be excluded from our enumeration of possible
causes of pain, especially when we remember that all
the neural phenomena
of health are carried on in the
presence of a certain varying but definitely limited pressure,
alteration of which, in the brain at least, is a fertile
source of mischief. How far these pressure conditions
may be needed for the proper functional life of the nerve,
we can hardly surmise; nor can we, in any case, separate
their probable influence from that of the nutritive supply,
which varies with them and ceases when they no longer
exist.
That sudden alterations of pressure may alone be suflScient
to painfully excite the nerves, is seen when a tourniquet
is removed after having been some hours on a limb.
Such a treatment was resorted to, many years ago,
for the