There are some ether but rarer and generally less serious cases of paralysis, in which no material change is discoverable in the structure of the nervous system. These are called functional or idiopathic paralysis ; but it may be reasonably doubted whether they do not all, or for the most part, depend on some alteration not yet discovered, and perhaps inappreciable by our present means of investigation. Such cases occur in some anomalous forms of nervous diseases, as in hysteria, and appear to be connected by sympathy with disorder of the uterine or digestive functions ; they are also not unfrequently pro duced by the introduction of poisons, as in those who work with lead or mercury.
General paralysis, in which all sensation and voluntary motion arc impaired or lest, is most commonly the result of apoplexy, or of severe injury to the head, producing concussion ar compression of the brain ; and indeed it may be said to exist in all cases of complete coma, or insensibility. More rarely it is produced gradually ; the patient. losing in succession the power of motion in all his muscles, and at last existing only with an internal life, but disabled from all active communication with the external world. This state is usually the result of disease of the brain or spinal cord gradually spreading through their substance; and especially of disease of the latter spread ing upwards. It not unfrequently comes on in the inmates of lunatic asylums.
The most frequent if not the only cause of paraplegia is injury or disease of the spinal cord ; and this may originate in its own struc ture, or be produced by injuries or diseases of the vertebral column or other parts surrounding it. Paraplegia, when the result of disease, commonly affects first the lower extremities and the parts below the level of the haunches, because the first part affected in the greater number of diseases is the lower portion of the spinal cord, frcm which the nerves supplying the lower extremities and pelvic organs are derived. When produced by injuries of the vertebral column however, the paraplegia may from the first affect the body to a much higher level ; its extent being always determined by the height in the vertebral column at which the injury is inflicted. In either case the disease, whether original or consequent upon injury, tends to spread up the cord ; and with a corresponding progress, the paralysis rises up the trunk, and affects successively the chest and arms, termi nating in death when the disease has reached the origin of the phrenic nerves, upon which the movements of the diaphragm depend.
In this form of paralysis, when all sensation and voluntary motion are destroyed, involuntary movements arc produced by irritating the skin of the insensible parts. These motions depend on the reflex actieu of the spinal cord [NEevous NAT. HIST. Dro.]; the power of conducting impressions to sod from the brain is lost, but the power which the cord possesses of exciting motions when impressions are made upon it, remains. The patient thus affected is indeed, as far as his nervous system is concerned, in the same condition as a beheaded animal; and the actions produced by irritating the parts below the divided or injured portion of the cord are of the same kind as those observed after decapitation.
In paraplegia the parts deprived of nervous connection with the brain are, even more than in any other form of paralysis, liable to mortification when long subjected to pressure ; and hence the slough ing of the back, which so commonly tends to shorten the patient's life. The sensibility to the pain produced by long-continued pressure being destroyed, the patient would not be inclined, even if he were able, to make those frequent changes of position by which a healthy person avoids its dangers.
Hemiplegia, in which the paralysis is confined to one side of the body, usually affects! (as paraplegia does) the sensitive and the motor nerves simultaneously. This is by far the most frequent form of para lysis, and is that by which those popularly called paralytic are usually affected. Hemiplegia generally occupies exactly one-half of the body, the middle vertical plane separating the healthy from the paralytic portion. It is at once easily recognised in any patient by the flatness and smoothness of the affected side of the face, by the angle of the mouth being drawn over towards the opposite side, and by a general wry position of the features. The arm hangs powerless by side; and in walking, the patient drags the affected leg after him, or, raising it from the ground by depressing the opposite side of the pelvis, lets it swing forward with its toe pointed towards the ground like a pendulum. Hemiplegia is most frequently the consequence of amrlexyrort.txri, remaining after the patient has recovered from the complete inseneibility or general paralysis by which the seizure was at find followed. More rarely it appears to rise from or diverganbetion of the brain, and is not preceded by any fit, but developed 17 degrees from slight to perfect loss of nervous power.