Krafft-Ebing agrees with Schüle in dividing mental diseases into two classes—those of a degenerative nature arising from the development of an hereditary or congenital neurotic tendency, or from injury, sexual or alcoholic excess, etc., and those which occur from what may be called accidental causes in otherwise healthy persons, in whom mental disease would not be anticipated, and from which the late Isaac Ray said that, with sufficient exciting cause, no one has any privilege of exemption. The essential distinction between them was pointed out by Moreau and Morel, and is best stated by Krafft-Ebing: Degenerative insanity is a constitutional disease arising from slight exciting causes, even physiological conditions (puberty, menstruation, the puerperal state, climacterium), but for the most part from pathological conditions, chiefly hereditary predisposition, injury to the head, acute disease, etc., occurring during development of the sensitive brain, forming often the last in a series of neuropathic disorders, such as spinal irritation, hysteria, hypochondria, epilepsy. The tendency to recovery is slight, and generally there is only temporary return to the primary condition. Relapses and progressive development of graver forms of disease are common. There is progressive hereditary mental degeneration or a strong tendency to appear in descendants in progressively severer form. All forms of the psychoneuroses occur, but of severe type and irregular course, with sudden and rapid changes in the character of the disease, which does not follow any particular course and cannot be definitely classified, rarely ending in dementia, and often lasting in some form through life. The tendency to periodicity is strong. Delusions are chiefly physio-pathological as direct creations of the diseased brain, entirely without apparent cause, to the astonishment of the person and independent of his frame of mind at the time. They appear and disappear, to be replaced by morbid impulses or mental weakness. Delusions are strange, mysterious, monstrous, without possible explanation from the {109} nature of the disease. There is, for the most part, an inseparable transition from pathological predisposition to actual disease, with a strange mixture of lucidity and diseased mental perversion. Acts are often from impulse. There are sudden outbursts or short attacks; as, for instance, in periodic, hysterical, and epileptic insanity.