The former differs from sane melancholy only in degree, and its chief characteristics are mental anguish and impulses to suicide. It includes probably one-half of all the cases of insanity, and is more frequently cured than any other form. In mania the morbidly elated mood may vary from excessive cheerfulness to violent rage. Monomania, which may exhibit characteristics of both melancholia and mania, is a perversion of the intellective rather than the affective faculties. Its chief manifestation is delusions, very frequently delusions of persecution.
Monomania corresponds roughly to the later and more precise term paranoia.
In this form the delusions are systematized and persistent, while the general intellectual processes may remain substantially unimpaired. When the attacks of melancholia or mania occur at regular intervals they are frequently named periodical insanity. The term partial insanity comprises chiefly those varieties known as impulsive, emotional, and moral. Somewhat akin to these forms are those associated with such general diseases of the nervous system as epilepsy, hysteria, and neurasthenia. When insanity takes the form of a general enfeeblement of the mental faculties as a consequence of disease, it is called dementia.