Insanity prevails not only at a time of life when the strain on mind and body is great, as is shown by the preceding table, but also in those places where the effort is most intense. That fact is well shown in the distribution of insanity over the State in the large and small towns, being greatest where the concentration of population brings with it extremes of poverty and wealth, as indicated by the following table, showing the number of admissions accredited to cities and towns in the McLean, South Boston, and State hospitals for the insane per 100,000 inhabitants from 1871 to 1880, the difference being exaggerated by the proximity of the hospitals and greater ease of commitment in the larger towns:

Number
of
Towns.		Population.Inhabitants
by Census
of 1875.		Insane
Patients.		Insane Patients
per 100,000
Inhabitants.
341The State1,651,9125689344
1Boston341,9191987581
1220,000 to 50,000405,6551486367
425000 to 20,000367,9571193324
2865000 and under536,3811023190

Of 9381 men and 9041 women admitted to our asylums, 7435 were married, 8193 single, and 1620 widowed or divorced. Of the 9381 males, 2215 were laborers, 1357 farmers, 313 clerks, 62 clergymen, 59 physicians, 43 lawyers, 201 students, of whom 114 were in school. Of 4673 females, 52 were school-girls.

The exciting or immediate causes of insanity are usually so complex that many of the statistics on that point conform to the preconceived views of the various compilers of them, as it is very easy to pick out a few from the many; but out of a large number of persons exposed to the alleged causes of insanity, one can never feel certain how many, nor indeed what, individuals will become insane.

It is not always easy to say how and when the furrows left in the brain by the mental and so-called moral causes of insanity have deepened into actual mental disease. Prolonged emotional and mental strain or severe mental shock often are directly associated with the immediate appearance of insanity. In armies, among people separated from their homes, in prisons, insanity oftener occurs than among the same people at home. Severe grief, disappointment, great and sudden joy or success, chagrin, fear, religious or political excitement, wars, pestilences, domestic or business troubles, poverty, and misfortune are among the commonly-reported moral causes of insanity, as are certain occupations involving steady and monotonous toil, especially if involving mental worry or necessitating unhappy relations.

Of the physical exciting causes of insanity, intemperance in the use of alcohol is easily first: luxury and excess in eating, drinking, and sexual indulgence, especially if associated with overwork or physical inactivity and mental anxiety, are also dangerous. It is difficult to estimate the influence of syphilis except when giving rise to coarse disease of the brain. Masturbation acts as an exciting cause, chiefly by creating a morbid psychical state and by exalting the sensibility of the nervous system, but probably not often, even with the young. Injuries to the brain and nervous system are usually slow in their operation, unlike the severe mental shock which is at once followed by insanity. Pain also, if intense, like great loss of blood, acts slowly by wearing out the powers of resistance, or rapidly by producing delirium.

A relation between pulmonary consumption and mental disease is frequently observed—partly, perhaps, due to general anæmia, in part to circulation of diseased blood in the brain, and partly from tubercular deposits. Other diseases act directly upon the brain and nervous system, as leptomeningitis, pachymeningitis, sclerosis, capillary aneurisms, embolisms, cerebral hemorrhage, tumors, disease of arteries, syphilis, caries, exostosis, abscess, internal otitis, sunstroke; still others by disturbances in the cerebral circulation, as diseases of the heart and kidneys; others by vitiating the blood circulating in the brain, as in the acute stage of febrile disorders; others in some general unknown way, as chorea, hysteria, epilepsy, gout, rheumatism, malaria, pneumonia; and still others during the period of convalescence or of general exhaustion, which is often associated with infectious diseases or chronic disease attended with general anæmia. The more violent and curable psychoses occur at the height of acute diseases, those of longer duration and of less favorable result during convalescence. Among other recognized causes are prolonged and obstinate dyspepsia, the psychological changes, if morbidly developed or attended with accident, at puberty, during pregnancy, at childbirth, during the puerperal state or lactation, and at the climacterium, and rarely various affections of the abdominal and pelvic organs.

Chronic alcoholism produces disease of the small blood-vessels of the brain and the consequences of that condition, causing insanity in a considerable proportion of cases, and almost always some mental impairment. Insanity occurs under conditions of cerebral hyperæmia and of cerebral anæmia, although their relation as cause and effect is very obscure. The habitual use of hasheesh gives rise to a disagreeable form of dementia, and so does opium, but more rarely. The effects of poisoning from iodoform, lead, mercury, bromide of potassium, hydrate of chloral, belladonna, tobacco, when reported as producing insanity, are usually transitory.

Cases have been reported of two persons being exposed to the same causes and having similar attacks of insanity (folie à deux), and also of folie induite or folie communiquée, where several persons have adopted the delusions of a person of influence among them, one of the most remarkable instances of which was the case of the seventeen grammar-school-taught Adventists of Pocasset, who accepted the insane belief of their leader, Freeman, that, like Abraham, he had been commanded by the Lord to kill his child, that she was to rise on the third day after he had killed her, and that he was to become a great evangelist. So-called epidemic insanity, choreomania, and demonopathy belong in this class.