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

18 INJURIES OF NERVES.
muscle would be remarkable,— a likeness, I may add, for
whicli there may also be some physiological foundation.
The mode in which the nerve tubule relates itself to
the centres and to the exterior organs
is full of interest.
It appears now to be pretty generally admitted that the
tubule may finally be traced into the cells of the ganglia
composing the spinal medulla and the brain, and that
before joining these cells it loses its sheath and white
covering, becoming thus reduced to the single element of
the axis cylinder. It has been inferred from this that the
latter part is the essential portion of the ultimate tubule,
and that the exterior portions are merely meant to serve
for protection or for insulation.
Observers are also well agreed that a similar loss of the
external medulla and sheath, and a like thinning of the
axis cylinder, is usually observable in the peripheral
extremities of nerve tubules; but the most extreme diversit}^
of opinion is held as regards the manner in wbich
they terminate and as to the relation they bear to muscle,
on the one hand, and to the sensitive surfaces on the
other.
Perhaps no questions in micrology have been less distinctly
answered than these. The mass of observers agree
that the sensitive nerves may be traced for the most part to
a plexiform series of loops which underlie the skin and
other sentient surfaces. According to Beale and some
others, these plexiform series constitute the true peripheral
termination of many sensitive nerves, which, returning
again to their central cell connections, form, as it were, a
neural circuit. On the extreme outer loops. Dr. Beale
located little masses of germinal matter, which he presumes
to have an office connected with the incessant
maintenance and increase of these ultimate loops,
— a view
which has been much controverted.
The appearances so described have of late been other-