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

NEURO-PHYSIOLOGY. 41
the peripheral nerves, no different channels for their
passage.
It is as if through a single tube were spoken various
languages which could be only understood when, at its
farther end, they reached the ear of the hearer native to
each form of speech. There is in physical science a good
deal in favor of the view I have so briefly urged, and,
clinically, something may be said for it.
We now know that motor-excitations may be made to
pass over sensory nerves, and vice versa, while in most of
the instances of loss of pain without loss of tact the lesion
has been plainly central. In the rare cases of peripheral
analgesia without anaesthesia, it is quite possible that such
modifications may have taken place in the nerves as to
have destroyed the power of the nerve tissues to transmit
particular forms of excitation.
Recurrent sensibility.
— Although we admit the general
proposition that the anterier roots of spinal nerves are
motor, and the posterior are sensory, there is an apparent
exception to this which has generally been admitted of
late years.
When we divide the posterior root of a spinal nerve, all
sensation is lost to the terminal branches of the mixed
nerve of which it makes a part. So also is motion utterly
lost by dividing the anterior root. If, however, the spine
has been opened with certain precautions, and the nerve
roots, after exposure, have been left at rest for a certain
time, it will be found that distinct evidences of sensibility
the anterior root. Should we
may be evoked by irritating
the central end will be found to
then divide this trunk,
possess no sensibility such as will exist in the peripheral
extremity, and section of the posterior root will abolish
altogether these evidences of feeling so that it becomes
;
clear that the fibres communicating sensation to the anterior
root must depend upon the posterior root.
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