In-săn i-tў. [Lat. Insa’nia, Insan’itas, a’ tis; from the same.] (Fr. Folie, fo’le’; Ger. Geisteskrankheit, ğīs’tes-krank’hīt, i.e., “sickness of the mind.”) Deranged intellect; madness, or lunacy. Insanity takes many forms, and may be due to a multitude of different causes. The most important predisposing cause is a tendency inherited from one’s parents or ancestors. When this tendency exists, any unusual excitement or strain upon the mind may develop the disease; which, indeed, may occur when it seems impossible to trace it to any exciting cause. Sometimes the disorder may pass over one generation and return in the third: thus, a grandparent may be afflicted with the disease, from which his children seem to be exempt, though his grandchildren may become its victims.

As a general rule, insanity is most likely to occur in those whose minds, from whatever cause, are subjected to intense or long-continued excitement: it is scarcely necessary to remark that the more susceptible the mind is to any kind of excitement, the more liable, other things being equal, it is to be affected with insanity. Hence we find that men in a rude or uncivilized state seldom suffer from this disease.

Intemperance is a prolific cause of insanity. The disease arising from this source is noticed under the head of ALCOHOLISM. Some writers classify the different forms of insanity, -1, as those caused by mental exaltation; 2, those arising from mental depression; and 3, those due to mental weakness. The first includes the various forms of insanity as this term is popularly understood; the second, the different forms of MELANCHOLIA; and the third, the affections known as DEMENTIA and IMBECILITY, or IDIOCY (which are noticed under their respective heads).

Source: Joseph Thomas, "A Complete Pronouncing Medical Dictionary: Embracing the Terminology of Medicine and the Kindred Sciences, with their signification, Etymology, and Pronunciation " (Philadelphia: J.B. Lippincott Co., 1893)

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