INSANITY, med. jur. A continued impetuositv of thought, which, for the time being, totally unfitsga man for judging and acting in relation to the matter in question, with the composure requisite for the maintenance of the social relations of life. Various other definitions of this state have been given, but perhaps the subject is not susceptible of any satisfactory definition, which shall, with, precision, include all cases of insanity, and exclude all others. Ray, Med. Jur. 24, p. 50.
2. It may be considered in a threefold point of view: 1. A chronic disease, manifested by deviations from the healthy and natural state of the mind, such deviations consisting in a morbid perversion of the feelings, affections and habits. 2. Disturbances of the intellectual faculties, under the influence of which the understanding becomes susceptible of hallucinations or erroneous. impressions of a particular kind. 3. A state of mental incoherence or constant hurry and confusion of thought. Cyclo. Practical Medicine, h. t.; Brewster's Encyclopaedia, h. t.; Observations on the Deranged Manifestations of the Mind, or Insanity, 71, 72; Merl. R«pert. mots Demenoe, Folie, Imbecilite; 6 Watts & Serg. 451.
3. The diseases included under the name of insanity have been arranged under two divisions, founded on two very different conditions of the brain. Ray, Med. Jur. ch. 1, 33.
4. - 1. The want of, or a defective development of the faculties. 1st. Idiocy, resulting from, 1. Congenital defect. 2. An obstacle to the development of the faculties, supervening in infancy. 2d. Imbecility, resulting from, 1. Congenital defects. 2. An obstacle to the development of the faculties, supervening in infancy.
5. - 2. The lesion of the faculties subsequent to their development. In this division may be classed, 1st. Mania, which is, 1. Intellectual, and is general or partial. 2. Affective and is general or, partial. 2d. Dementia, which is, 1. Consecutive to mania, or injuries of the brain. 2. Senile, or peculiar to old age.
6. - There is also a disease which has acquired the name of Moral insanity. (q. v.)
7. Insanity is an excuse for the commission of acts which in others would be crimes, because the insane man has no intention; it deprives a man also from entering into any valid contract. Vide Lunacy; Non compos mentis, and Stock on the Law of Non Compotes Mentis; 1 Hagg. Cons. R. 417; 3 Addams, R. 90, 91, 180, 181; 3 Hagg. Eccl. R. 545, 598, 600; 2 Greenl. Ev. 369, 374; Bouv. Inst. Index, h. t.