A. Cysts

Even in the trunks of very large nerves such formations are extremely rare. It is at once clear from the conditions under which the cyst is developed that it performs the office of a bursa.

B. Fibroid Tissue

This structure is met with in nerves chiefly as a product of inflammation. But there are also certain tumors which are known generally by the name of neuroma, and which appear to me to rank with fibroid structures. When they exist in great number, as they sometimes do, pervading many, or most, or even all of the nerves, they constitute that which Serres has most erroneously denominated a change of the nerves to ganglionic structure.

Neuroma is the most frequent adventitious growth, except cancer, which occurs in the peripheral nervous system; and cancer is very frequently only a secondary affection in which nervous tissue is involved in consequence of its contiguity to other diseased organs.

Neuroma forms round, or more usually elongated and oval, tumors, the long diameter of which is parallel to the nerve. They are of a tough elastic consistence, and of a grayish or pale yellowish-red color, and are invested with a distinct fibrous sheath. In size they vary from a scarcely discernible enlargement of the nerve, to the bulk of a walnut or even of a hen's egg, and in number, from one until they are almost countless. In this last case neuroma constitutes a very remarkable general disease, as to the cause of which we are still in the dark. It has already been observed several times, and three times in the Vienna Hospital. It has been noticed in such cases, that the size of the tumor bears no direct proportion to the thickness of the nerve on which it is formed, for in fact those tumors which are situated on small branches are relatively much larger than those which occupy the thick trunk of a nerve.

The tumors lie between the fasciculi of the nerve and are interwoven" with their neurilemmatous sheath. And it is a remarkable, and no less important general rule, because of the symptoms which may result from its presence, or which may be set up by operations performed on it, that neuroma is never deposited in the centre of a nerve, but at its side, so that only a small part of its fasciculi is displaced; the displaced fasciculi are spread abroad and stretched over the tumor, while the greater mass of the nerve remains on the other side uninjured, and with its fibres in connection with one another.

Neuroma occurs most frequently in the spinal nerves and in those cerebral nerves, motor as well as sensitive, which resemble the nerves of the cord: it may occur at any point in their course, even within the canal of the dura mater of the cord, and close to their junction with the medulla.

Although neuroma, when a solitary tumor, frequently occasions very considerable annoyance and pain, yet such is by no means invariably the case; and in those instances in which neuromatous growths were extensively diffused through the nervous system they had given rise to no symptoms whatever.

c. I have never met with any instance of anomalous bony substance, or so-called ossification, in nerves, although the callus remaining in them after inflammation, and neuromatous tumors, seem to furnish a suitable foundation for the production of it.

d. Nerves may be destroyed in the softening of tubercle either around or adjoining them, though the larger nerves resist tubercular and all other suppurative destruction for a long time. Nerves are never the seat of primary tubercle. With cancer, however, the case is different.

e. Cancer often occurs in the peripheral nervous system as a secondary disease, the nerve yielding to the aggression of a neighboring cancerous growth: and not unfrequently it presents itself as a primary disease. In respect to the former, the secondary affection, - when any organ is the seat of cancerous degeneration, the nerves included in it may be destroyed in the same manner as other tissues; or a cancerous mass, as it advances, may involve any nervous trunk that lies upon it.

Whether the nerve be primarily or secondarily diseased, the form of the cancer is generally the medullary; indeed, the white medullary cancer and melanosis appear to be the only forms with which nerve is primarily affected. Although a nerve when secondarily affected with any kind of cancer, is attacked, as a general rule, in the same manner as any other tissue, yet it is remarkable how little resistance it appears to offer to the inroad of medullary cancer in particular.

Primary cancer may be developed at the peripheral extremity of a nerve, or at any other spot in its course, up to its termination in the nervous centre. The former is by far the most frequent situation, and the best known example of it is medullary cancer of the retina.

Medullary cancer of nerve, as that of the retina shows, commonly reaches a very large size. Very often it is quite alone in the system, though not unfrequently it is combined with cancer in other organs. Thus cancer of the optic nerve within the skull, and of the brain, often coexists with cancer of the retina. The extirpation of fungus bulbi, or primary cancer of the retina, is, as a general rule, succeeded by a very rapid and extensive (tumultuous) development of cancer in several organs at once.