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

74 INJURIES OF NERVES.
the subject of the wasting of nerves and of their repair
presented no great interest until the classical researches of
Augustus Waller, in 1862. This admirable observer has
been happy in the almost perfect accord with which his
researches have been met whenever they have been experimentally
examined by competent inquirers. Since a
clear knowledaje of his conclusions lies at the basis of the
subject of nerve changes after section, I shall endeavor to
give a brief and distinct account of these results.
Section of a nerve trunk, whether it be sensitive, motor,
or of double function, insures degeneration of the peripheral
extremity. If, however, we divide the sensitive
filament (posterior root) of a spinal nerve between the
ganglion and the spinal cord, the central end alters and
the portion attached to the ganglion remains unchanged.
Section of the motor (anterior) root, between the spine
and its union with the posterior root, gives us degeneration
of the external end and no alteration of the central
extremity. Connection with the spine or the ganglion
seems, therefore, to insure against degeneration the anterior
or posterior root respectively. "Waller himself believed
that the ganglion
is the trophic, or nutritive, centre for
the posterior root, and that the gray spinal matter, in like
manner, holds the same office for the anterior root. Physiologists
have, however, hesitated to accept this theory,
while the facts themselves have remained undisputed.
Whenever section of a compound nerve has been made
exterior to the ganglion, the entire peripheral end of the
nerve alters, and the central end remains unchanged.
To this law, Laverran* has pointed out a supposed exception.
In the central end of cut nerves he found a
few altered fibres, and in the peripheral end, a certain
number of sound fibres. The degenerating fibres of
* Laverran, These de Strasbourg, 1864.