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

16 INJURIES OF NERVES.
geneous, yet at places longitudinally striated, substance,
dotted more or less with nuclei and with minute gray
molecular granules.
When the primitive bundles of nerve fibres exchange
filaments with others, as in a plexus, their peculiar sheaths
accompany them until the single nerve tubules approach
a free termination, when the sheath ceases to be visible.
Should the tube end, however, in a corpuscle of Pacini,
the sheath is continuous with that which covers these
bodies. Neither nerves nor vessels have, in man at least,
been traced into these ultimate sheaths.
Within this covering pass the ultimate nerve tubules,
the structure of which has been the subject of numerous
investigations.
According
to the latest authoritative observers,
the nerve tubule consists of four distinct parts :
1st. The sheath of Schwann, or tubular membrane.
2d. The medullary matter, or white substance of
Schwann.
3d. The axis cylinder.
4th.
The elements of the axis cylinder, which may be
one or many fibrils.
This complex structure
only becomes visible in consequence
of post-mortem changes or the action of reagents,
so that the fresh nerve fibre looks like a pellucid rod.
The sheath of Schwann is described as a thin, delicate
membrane, only perceptible when torn or treated by
reagents, or when excessive atrophy has removed its contents.
Within this envelope is found the medullary matter,
which is transparent, semi-fluid, and of a high refracting
power, which gives to it the appearance of possessing a
double contour or outline. In chemical composition
it is
undoubtedly fatty. It is this substance wdiich gives to the
nerves a white hue, and the absence of which causes them
to look translucent or gray. It is
wanting
nerves.
in certain