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 origin (vide figs. 2, 3, 4, and 5). Alcoholic polyneuritic psychosis affecting women in many ways resembles delirium tremens; the fact that neuritis occurs much more frequently in women is probably associated with a greater liability to the influence of microbial toxins by absorption from the organs of reproduction. Many other poisons, notably lead and arsenic the specific fevers before mentioned, syphilis and alterations of the blood due to imperfect metabolism, such as occur in diabetes and gout, may produce, or become important factors in producing, peripheral neuritis. The outbreak of arsenical neuritis from beer containing this poison in Manchester in 1900 is of interest, from the fact that the symptoms closely resembled acute alcoholic neuritis. A distinctive feature, however, was the pigmentation of the skin and the severity of the nervous symptoms. A disease which is common in the East, termed Beriberi, is a form of neuritis, the cause of which is not exactly known (see ). Anaesthetic leprosy is an interstitial inflammation of the nerves due to the Lepra bacillus. Among the nervous diseases due to occupation may be cited lead-poisoning. This is peculiar in selecting the nerve which supplies the extensor muscles of the wrist and fingers, so that dropped wrist is almost characteristic of this form of toxic neuritis. Lead also produces a chronic inflammation of the cerebral cortex, Encephalitis saturnina, causing a complex of symptoms, namely, dementia, loss of memory, weakened intellect, paresis and epileptiform seizures, hallucinations of sight and hearing, and mental exaltation or depression. Mirror-makers suffer with characteristic fine tremors, from the slow absorption of mercury into the system. Workmen at indiarubber factories may suffer from severe mental symptoms, owing to the inhalation of the fumes of bisulphide of carbon. Serious nervous symptoms have followed carbon monoxide poisoning. Cases which have recovered from the immediate effects have suffered with dementia and symptoms of disseminated sclerosis, the result of multiple haemorrhagic softenings.

There are a certain number of poisons, besides alcohol, which act upon the nervous system when continually entering the body as the result of a habit, namely, absinthe, ether, cocaine, opium, morphia, hashish and tobacco. Each of these poisons produces a train of symptoms denoting a selective influence upon certain parts of the nervous system. In illustration thereof may be mentioned impairment of central vision in tobacco amblyopia.

The disease pellagra, an affection of the skin associated with degenerative changes in the brain and spinal cord and characterized by melancholy with suicidal impulses, sometimes mania associated with paresis, was long considered to be due to the eating of bad maize. But in 1910 the recent research on this disease, still in progress, seemed to negative this theory (see . Another disease, ergotism, in an epidemic form, has affected poor people in Russia and North Germany when obliged to subsist upon bread made of rye which has been attacked by the ergot fungus. The poison thus introduced into the system produces progressive degenerative changes in the brain and spinal cord, which are manifested by psychical disturbances, such as slowness of thought, weakness of memory, dulness of perception, sometimes delirium and incoherence; other symptoms are blunted sensibility, dilated pupils, muscular spasms, perhaps even epileptiform seizures and ataxy, and, lastly, stupor deepening into coma. Sausage disease, due to eating decayed meat and fish infected with Bacillus botulinus, is associated with symptoms which frequently terminate fatally, and it has been shown that the symptoms are due to a poison which has a very destructive effect upon the nerve cells (fig. 6).

II. Normal and Abnormal Stimulation.—The nervous system, in order to develop and manifest functional activity, requires suitable stimulation from without. Structure and function are mutually reciprocal and interdependent; for a structure which is not used will gradually lose its function, while its nutrition will also suffer, and in time atrophy may occur. Consciously and unconsciously, a continuous stream of impulses is pouring into the nervous system from without by the sensory channels, which are the avenues of experience and intelligence, and our somatic and psychical life depends upon the existence of such stimuli. The nervous system in the form of systems, groups and communities of neurones, each with special functions, yet all woven together in one harmonious whole, develops in a particular way in consequence of the awakening influence of these stimuli from without. Consequently nervous structures which are not used are liable to undergo regressive metamorphosis and atrophy; thus amputation of a limb in early life causes atrophy of the nervous structures which presided over the sensation and movement of the part. This is seen both in the grey and white matter of the spinal cord; there is also an atrophy of the psychomotor neurones of the brain presiding over the movements of the limb.

A healthy physical, intellectual and moral environment of the individual is an essential factor in the prevention and cure of psychoses and neuroses, because it tends to develop and strengthen body and mind, deliberation, judgment and the higher controlling functions of the brain. A function not used will gradually disappear, and become more and more difficult to evoke. This fact is of importance in functional neuroses and psychoses, e.g. hysterical paralysis, melancholia and delusional insanity, because the longer mental or bodily function is left in abeyance, the more likely is the defect to become permanently installed. The converse is also true; the longer a perverted function exists, the more unlikely it is to disappear. Thus auditory hallucinations, a very important and frequent symptom in the insane, commence with indistinct noises: these are followed by “voices,” which eventually become so distinct and real that the greater part of the patient’s psychical existence is concentrated upon, and determined by, this abnormal stimulus from within, indicating progressive strengthening and fixation of the perverted functions of the mind, and progressive weakening and dissolution of the normal functions.

Mental pain in the form of grief, worry, anxiety, fright, shock, violent emotions (pleasurable or painful), disappointed love, sexual excesses or perversions, and excessive brain work, frequently precede and determine, in persons with the insane or neuropathic taint, various forms (a) of psychoses, e.g. mania, melancholia, delusional insanity; (b) of neuroses, e.g. chorea, hysteria, epilepsy, hysteroepilepsy; (c) or organic brain disease, e.g. apoplexy, thrombosis, general paralysis.

Visceral reflex irritation affords many examples of neuroses and psychoses, the symptoms of which are 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 convulsions, spasms of the glottis and tetany. Various functional and organic