The influential system put forward by Kraepelin unified nearly all types of mood disorder into manic-depressive insanity.

Another set of diagnoses that appeared to have a periodic course and better outcome were grouped together under the category of manic-depressive insanity (mood disorder).

Kraepelin devoted very few pages to his speculations about the etiology of his two major insanities, dementia praecox and manic-depressive insanity.

Or, more likely, manic-depressive insanity, the folie circulaire type: recurring periods of maniacal excitement alternating with periods of the clearest sanity, don't y' know.

Dementia praecox was reconstituted as schizophrenia, paranoia was renamed as 'delusional disorder' and manic-depressive insanity as 'bipolar disorder' (epilepsy was transferred from psychiatry to neurology).

In his collection of essays on genius the distinguished neurologist, the late Sir William Russell Brain, concluded about Smart that 'clearly he suffered from manic-depressive insanity or cyclothymia' and there is much to support that diagnosis.

What is known for sure is that by the turn of the 20th century the old concept of insanity had become fragmented into 'diseases' (psychoses) such as paranoia, dementia praecox, manic-depressive insanity and epilepsy (Emil Kraepelin's classification).

He rejected Kraepelin's division of the functional psychoses into two divisions: dementia praecox (later renamed schizophrenia) and manic-depressive insanity, and attempted to isolate a large number of disease entities which he believed were due to focal brain lesions.