1. Congestion - Apoplexy

It may be that nerves are not unfrequently congested; but there is scarcely ever opportunity in the dead subject to see any such condition of either their trunks or branches, except what has occurred since death.

More important instances of hyperemia are found in the sympathetic system; its central ganglia becomes congested in the course of general acute processes of low type (dyscrasisch), which become localized in those structures to which the ganglionic nerves are distributed, especially in the mucous membrane and follicular apparatus of the intestines. The congestions of the ganglia just mentioned in the early stages of ileo-typhus, in the course of cholera and cholera-typhus, are of this class.

These congestions sometimes lead to apoplexy. In that case (during the same processes), the ganglia are found ecchymosed, or dotted with little round spots or streaks of extravasated blood, which are of about the size of a millet-seed.

2. Inflammation

Inflammation may be observed in nerves as a consequence of injury, especially after they have been cut through: and in the trunks of larger nerves, such as the sciatic, rheumatic inflammation is met with in the dead subject. Inflammation may also pass over to nerves from adjoining tissues.

Its general characters are those of inflammation of fibrous tissue, inasmuch as its seat is the neurilemmatous sheath. When it is very intense, the characters of the red softening of nervous tissue are added. Its course is sometimes acute, sometimes chronic.

The marks of acute inflammation are as follow:

A. Injection

Injection, which presents a linear arrangement; and redness, which proceeds partly from the injection, and partly from small extravasations by which the neurilemmatous tissue is streaked and dotted.

B. Looseness, Succulence, And Swelling Of The Nervous Cord

Looseness, Succulence, And Swelling Of The Nervous Cord, which result from the infiltration of serum into the tissue of the neurilemma, and into the sheaths between the primitive filaments. The fasciculi diverge manifestly from one another, and the nerve appears unravelled; and when the actual exudation is effused, this character is still more marked. The nerve has lost its smooth white glistening appearance; and its neurilemma is opaque, and appears rough and wrinkled.

C. Exudation

This is generally a grayish- or yellowish-red, gelatinous product, which sooner or later becomes firm. It is effused into the sheaths and tissue of the neurilemma, as well as between the primitive filaments themselves.

The intensity of these appearances varies widely. The redness may be a slight rosy tint arising from injection, or a deep saturated red color; it may be composed of some injected varicose branches, or of confluent ecchymoses. The swelling also may be of any degree, according to the quantity of the exudation. And further, the process may be merely confined to the outer layer of neurilemma, or it may extend more or less deeply to the sheaths of the several fasciculi.

D. The Cellular Tissue

The Cellular Tissue around the nervous cord always shares in these changes; it becomes injected, reddened, and infiltrated with a serous or sero-fibrinous brine-like fluid. The inflammation may even extend to the sheaths of neighboring muscles, to the fascia, subcutaneous cellular tissue, and general integuments.

This degree of inflammation may terminate quickly or slowly by resolution; or in induration of the nerve and a permanent abrogation of its function in whole or in part. The products of the process remain behind in the form either of a hardened blastema or of filamentous tissue; the nerve continues thickened, and more or less misshapen, and forms a grayish cord, which is sometimes marked with black pigment, and crossed by varicose vessels; the fasciculi coalesce, and the nerve itself adheres to the parts around. The nerve-filaments diminish in size and finally disappear, partly because of the pressure to which they are subjected by the exudation in which they are enveloped, especially as after a time it begins to contract; and partly because their nutrition is interrupted; for the vessels are obliterated by the inflammatory process, or are usurped by the exudation.

e. By higher degrees of inflammation and by a rapid and copious (tumultuous) exudation, the primitive filaments of the nerve are destroyed. They are found colored, and in a state of red, or of grayish- or yellowish-red softening, whilethe neurilemmatous sheaths have become easily lace-rable. Such a condition may sometimes be seen in cases of spontaneous inflammation, but it is more common when the inflammation has succeeded injury. The exudation is generally purulent.

f. When this is the case, that is, when the exudation is purulent, the nerve appears highly discolored, and is infiltrated with a purulent fluid mixed with blood; its neurilemma is as fragile as tinder, and is losing its vitality, while the mass of the nerve is changed into a yellowish-red, brownish-red, or chocolate-colored pulp. The cellular tissue around the nerve becomes infiltrated with yellow fibrinous exudation, and abscesses of various size are formed here and there in its course.

The next step in such an inflammation is an ulcerative destruction of the nerve. But should it stop short at this point, granulations appear, which become progressively changed into cicatrix tissue; just as is observed in the stump of a nerve after amputation. It must, however, be remarked that the nerves resist, for a long time, the suppurative and sanious destruction which may be going on around them. Chronic inflammation is characterized by the varicose state of the vessels of the affected nerve, by products which become indurated, and gradually increase in quantity, and by a change of the nerve to a slate-or lead-gray color. Sometimes the products are not deposited uniformly throughout the nerve, and then nodular swellings are formed on it.

There is one appearance which I must here mention as an appendix to the foregoing descriptions; it is the following condition of the nerves in cases of traumatic tetanus: and, however insignificant and unsatisfactory it may seem when brought into connection with the symptoms during life, yet it is the only real fact that has been made out in such cases after death. Froriep has ascertained that, besides the inflammation which is seen in the nerve at the spot which has been injured, a rosy reddening is produced at irregular intervals in its course by the injection of its neurilemma, but it is unaccompanied by any distinguishable products. The reddening is mostly confined to the surface of the nerve, though it sometimes dips a little way between the fasciculi. If a plantar nerve, for instance, has been injured, it is repeated three, four, five, or more times in the course of the tibial and sciatic nerves up to the sacral plexus; but neither where these nerves enter the medulla nor in the cord itself is any similar appearance to be found.