Periscope of Medical and General Science in their Relations to Dentistry. [Volume: 2, Issue: 11, June, 1861, pp. 625-637]

PERISCOPE OF MEDICAL AND GENERAL SCIENCE.

625

PERISCOPE OF MEDICAL AND GENERAL SCIENCE IN THEIR
RELATIONS TO DENTISTRY.
BY GEO. J. ZIEGLER, M.D.
Recurrent Sensibility.-After some general remarks on the comparative anatomy of the medulla spinalis, and the precautions necessary in
operative physiology, M. C. BERNARD makes the following observations
upon this subject in his lectures on the nervous system in the Med. Times
and Gazette: " When proper care has been taken to avoid the abovementioned difficulties, the existence of recurrent sensibility, as a constant
property of the motor branches, will easily be ascertained. The operator having laid bare one of the spinal pairs, the animal evinces acute
pain when either of the roots is excited; so that, in the normal condition, both orders of nerves are evidently endowed with a high degree
of sensibility. The anterior root being now divided, its peripheric extremity will be found sensible to various kinds of stimuli, while the central portion remains unaffected; such is the phenomenon which has been
described under the name of Recurrent Sensibility. It is evidently
derived from the influence which sensitive nerves exert over the corresponding motor branches; for, as soon as the posterior root is divided,
all sensation is at an end in the motor nerve, and the central portion of
the sensitive root, which lies in contact with the spinal marrow itself,
alone retains its characteristic property.
"The absolute independence of each nervous pair, taken individually,
is evidenced by the fact that recurrent sensibility still continues to exist
in a motor nerve when the pair which lies above and that which lies below it have simultaneously been divided. As long as the corresponding
posterior root remains uninjured, the sensitive powers of the motor nerve
retain their usual force.
" This singular property, which invests the motor branches with faculties derived from the sensitive apparatus, is to all appearance derived
from the anastomoses which take place between their terminal extremities; it has also been supposed that, after reaching the surface of the
body, certain sensitive filaments are conveyed back to the nervous centre
along the motor branches. It is, at all events, an indisputable fact, that
the exchange of nervous fibre does not immediately take place after the
junction of the spinal roots, but occurs at a much greater distance; for,
if the mixed nerve which passes through the intervertebral aperture is
divided, recurrent sensibility is abolished in the corresponding spinal
root.
* * * * * * * * *
"Among the various experiments which have led us to more accurate
notions concerning the functions of the spinal cord, the first in date as
well as in importance, is that which consists in setting forth the difference
between motor and sensitive nerves, by separately dividing the anterior
and posterior spinal roots. In demonstrating so elementary a proposition, it is hardly necessary to employ animals belonging to the higher
classes: the lower orders of vertebrata exhibit this property in the same
degree; and although the operation has usually been performed on
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