The nerves which form the very complicated system of gelatinous cords of various sizes which emanate from the brain and the spinal cord, send thousands of branches throughout the entire body. They communicate the impressions from the outside to the brain and convey its conscious or unconscious (instinctive) mandate to the muscles of all organs.
The nerves are fed by the lymphatic system and are everywhere accompanied by blood-vessles, and the oxygenous blood in the latter conveys the oxygen to the nerve substance, which it consumes and thus develops power sufficient to execute the various functions.
Naturally the supply that replaces the burned nerve substance, must be adequate, and if for any reason whatsoever more nerve substance is consumed than the body is able to renew by the time it is needed, the nerve system becomes degenerated and numerous disturbances are the consequence.
This is the great field of mental functions and disturbances, of moods and reactions on muscular tracts which in themselves are healthy, but are paralyzed in their work through the defective functioning of the power-conveying nerves.
Again it is impossible here to give more than a general description, showing on what conditions nervous diseases are based. The manifold manifestations of this degeneration were combined into groups under the old system in which the Greek name of a system was everything, its practical explanation but little.
The principal ways in which these degenerations manifest themselves are pains, mental agony and derangement, temporary cessation of functions, cramps, involuntary movements and similar disturbances.
The names generally applied to them are neuralgia and neuritis,—causing pains in the nerves of certain parts of the body; neurasthenia,—consisting mainly of the complete relaxation of tension in the nervous system, causing sadness, inability for work, etc.; asthma, cramp-like cessation of certain functions of the small vessels of the lungs, alveoli, which impedes respiration; epilepsy, temporary cramp in the greater part of the body, causing loss of consciousness, involuntary movements of the limbs, etc.; St. Vitus’s dance,—a similar affection, usually in children.
While the complicated nature of nerve diseases requires very careful treatment of great individual variety, the general rule is that the re-enforcement of the nerves with the material of which they are built, together with regeneration of the blood, which, when in normal condition prevents such disturbances, will bring about a cure. Of course this is sometimes a slow process, especially when, as in the case of epilepsy, the nervous disease is of an hereditary character, and the resistant power of the nerves is correspondingly weak.
In regard to one of the most disastrous diseases, caused by degeneration of the most important nerve i.e. the Vagus, see under “Catarrh”—section VI.