Neuropathology

Certain other poisons, besides alcohol, act upon the nervous system when continually entering the body as the result of a habit, namely, absinthe, ether, cocaine, opium, morphin, hashish and tobacco. Each of these has a selective influence upon certain parts of the nervous system. In illustration thereof may be men tioned impairment of central vision in tobacco amblyopia. Other diseases of like kind are under pellagra (q.v.), ergot (q.v.), botu lism (see MEDICAL RESEARCH).

Adequate and Pathological Stimulation.

The nervous system in the form of systems, groups and communities of neu rones, each with special functions, yet all woven together in one harmonious whole, develops in a particular way in consequence of the awakening influence of stimuli from without and from accu mulated instinct stimuli from within. Consequently nervous struc tures which are not used at all, or badly used are liable to undergo regressive metamorphosis and atrophy; thus amputation of a limb in early life causes atrophy of the nervous structures which dealt with the sensations and movements of the part. This may be seen in the grey (synapses) and white matter (conducting pathways) of the spinal cord; there may also be found an atrophy of the psycho-motor neurones of the brain functionally related to the sensory and motor terminal areas of the involved limb. The con verse is also true ; the longer a perverted function exists, the more unlikely it is to disappear and ultimately to bring about irrevers ible structural changes.

Mental pain in the form of grief, worry, anxiety, fright, shock, violent emotions (pleasurable or painful), disappointed love, and excessive intellectual work, frequently precede and determine various types (a) of psychoses, e.g., manic-depressive, paranoid; (b) of neuroses, e.g., compulsion neurosis, hysteria, epilepsy, hystero-epilepsy ; (c) or gross brain disease, e.g., apoplexy, throm bosis, arteriosclerotic degenerations.

Visceral reflex irritation affords many examples of organ neu roses, the symptoms of which may be set up by irritation of the viscera, e.g., intestinal worms. Teething and indigestible food are often the exciting cause in infants and young children of convul sions and spasms of the glottis (spasmophilic). Some anomalies of the female reproductive organs act as exciting causes in the re lease of hysterical reactions. Paroxysmal exacerbations of emo tional disturbances are liable to occur at the menstrual period or menopause. Here the stimulus proceeds from the reproductive

instinct. The irritation of a carious tooth may produce spas modic tic or trigeminal neuralgia. Wax in the ear may occasion vertigo and tinnitus; and grave errors of refraction in the eyes may be an accessory factor in the causation of attacks of migraine. Irritation of the receptors of the vagus in almost any part of its widespread visceral origin may lead to vomiting. The characteristic pain of angina pectoris, which radiates down the inner side of the left arm, is partly explained by the fact that the cardiac branches of the sympathetic follow the vascular supply of the arm, and the stimulus from the diseased aorta or coronary vessels radiates as pain in the vascular area. The entire explanation is extremely complex'. This is one example of a great number of referred pains studied so extensively by the English observers, Head and Mackenzie.

'Spiegel, Wien, Kl. Woch. 40, 1927, 853.

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 damage of the en closing structures or even the central nervous system. Shock, due to concussion, can thus be explained as resulting from molecular or bio-chemical changes in the nervous structures.

Direct injury may cause local destruction of the nervous tissue ; but wounds and diseases of the enclosing and supporting struc tures, if non-infective, give rise only to such symptoms as accord with the nerve structure irritated or destroyed. Should, however, the wound or diseased structure become infected, the disease spreads and becomes generalized ; likewise the symptoms. Of the many causes of infective inflammation of the brain itself, middle ear disease is the most important. It is very liable, when neg lected, 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 involve other parts of the brain as well, for example the cerebellum and frontal lobe. 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.