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 diseases of the female reproductive organs act as exciting causes in the production of hysteria, hystero-epilepsy, melancholia and mania; moreover, paroxysmal attacks in these diseases are more liable to occur at the menstrual period or menopause. The irritation of a carious tooth may produce spasmodic tic and trigeminal neuralgia. Wax in the ear may occasion vertigo and tinnitus; and errors of refraction in the eyes may be the cause of attacks of migraine, and even tend to excite epileptic fits in a person suffering from epilepsy. Numerous other examples of peripheral disturbance could be mentioned as exciting causes of nervous affection in neurotic individuals. Irritation of the terminals of the vagus in almost any part of its widespread visceral distribution may lead to vomiting. The characteristic pain of angina pectoris, which radiates down the inner side of the left arm, is explained by the fact that the cardiac branches of the sympathetic arise from the same segments of the spinal cord as the sensory branches of the ulnar nerve; consequently the pain is referred to the corresponding skin area supplied by this nerve. This is one example of a great number of referred pains.

III. Injury or disease of enclosing or supporting structures may lead to paralytic or irritative lesions of the nervous system, or the two may be combined. Blows or wounds of the head and spine may damage or destroy the nervous structures by shock or direct injury. Concussion of the brain or spinal cord may occur, as a result of injury, without any recognizable serious damage of the enclosing structures or even the central nervous system. Shock, due to concussion, can only be explained by a molecular or bio-chemical change in the nervous structures.

Direct injury or a fall fracturing the skull, driving the fragments into the brain, will cause direct destruction of the nervous tissue; but wounds and diseases of the enclosing and supporting structures, if producing simple non-infective inflammation, give rise only to such symptoms as accord with the nerve structure irritated or destroyed. Should, however, the wound or diseased structure become infected with micro-organisms, the disease spreads and becomes generalized likewise the symptoms. Of all the causes of infective inflammation, middle-ear disease, on account of its frequency and insidious onset, is the most important. It is very liable, when neglected, to be followed by a septic meningitis, encephalitis and brain abscess, the most frequent seat of which is in the adjacent temporal lobe, but it may be in other parts of the brain, e.g. the cerebellum and frontal lobe (Plate I. fig. 3). The peripheral nerves may be destroyed or irritated by direct injury, disease or new growth in adjacent tissues, or they may be involved in the callus thrown out round the seat of a fracture.

Diseases of the blood-vessels are among the most frequent causes of organic brain disease. Arteries or veins—more frequently the former—may become blocked or ruptured from various causes. The immediate effect is a disturbance or loss of consciousness, and the individual may be “struck down” (see ) and never regain consciousness (see ). Should the individual recover consciousness more or less permanent loss or disturbance of function will be the result. Paralysis of some form, especially hemiplegia, is the commonest result, but the loss or disturbance of function will depend upon the seat of the injury.

The cerebral arteries may be occluded by embolism; a portion of a clot or vegetation from a diseased valve of the left side of the heart may be detached, and escape into the circulation; and this is carried into one of the arteries of the brain, usually the middle cerebral, more often of the left side than the right. The area of brain tissue supplied by that artery is deprived of blood, and undergoes softening in consequence, resulting in paralysis of the opposite half of the body (hemiplegia) associated with aphasia when the paralysis affects the right side in a right-handed person (Plate I. figs. 5 and 9). When the embolus is infective, as it frequently is in ulcerative endocarditis, its lodgment in an artery of the brain, not only blocks the vessel but leads to an infective inflammation and softening of its coats, with the formation of an aneurism. The aneurism may suddenly rupture into the substance of the brain and produce apoplexy. In fact the majority of cases of apoplexy from cerebral haemorrhage recurring in young people are due to this cause. Softening may also arise from coagulation of the blood (thrombosis) in the arteries or veins. There are many causes which generally combine or conspire together to produce thrombosis, viz. a weak acting heart and altered conditions of the blood, and sometimes independently of vascular disease spontaneous coagulation in a vessel of the brain may occur. It is sometimes met with in the cachexia of certain grave diseases, viz. in phthisis and cancer, in typhus and pneumonia, after parturition and in marasmus at all periods of life, but especially in the very young and very old. But thickening, roughening and a degenerated condition of the cerebral arteries known as atheroma when associated with a weak acting heart is especially liable to give rise to thrombosis and softening, and this is a very common cause of apoplexy, paralysis and dementia in people who have passed middle life. General disease of the arteries of the body, associated especially with chronic Bright’s disease and high arterial pressure, is frequently attended with the formation of minute miliary aneurisms upon the cerebral arteries, which may rupture and cause apoplexy. Haemorrhage into the brain from this cause is especially liable to occur in certain situations; one vessel in particular, supplying the basal ganglia, most frequently gives way, the effused blood tearing through the motor efferent fibres, which, proceeding from the cerebral cortex in the shape of a funnel, become aggregated together to form the neck between the two masses of grey matter—the optic thalamus and the corpus striatum (Plate II. fig. 6). The result is hemiplegia of the opposite side of the body. Disease of the arteries of the central nervous system, occurring in a person under forty, is generally due to syphilis, the virus of which produces an inflammation of the coats of the vessel, especially the inner (see Plate II. figs. 4, 9, 10). The thickening and narrowing of the lumen with loss of elasticity of the arteries of the brain generally, may suddenly or gradually set up conditions of cerebral anaemia and give rise to semi-comatose and comatose or even apoplectic states. Occlusion by the inflammatory proliferation or by the sudden clotting of blood in the diseased vessel may occur, the immediate effect of which may be an epileptic or apoplectic fit; the result is softening; and seeing that any or all the arteries of the brain may be affected successively, simultaneously, or at random, the symptoms may be manifold. They may be general or local, and not uncommonly are associated with inflammation of the membranes. The disease, under treatment, may abate, and the paralytic or mental phenomena partially or completely disappear, indicating the restoration, or partial restoration, of the circulation in the diseased arteries; sometimes with the lapse of treatment and sometimes without, new symptoms, such as paralysis of a fresh group of muscles or of the opposite side of the body, may manifest themselves, showing that the disease has attacked a fresh set of arteries. Disseminated sclerosis (insular) is another random morbid process, affecting especially the white matter, with certain characteristic symptoms of a progressive character, the pathology of which is not understood fully, but is probably due to some toxic cause. Islands of nervous tissue undergo a morbid change, commencing in