Affective disturbances are a common consequence of organic brain lesions of varying aetiology, and it is to be expected that the differentiation between affective symptoms of “functional” origin and those resulting from organic lesions would become an increasingly difficult problem in an age-range which is particularly susceptible to pathological cerebral changes. In fact the classical accounts of mental disorder in old age convey the impression, by their emphasis on the depressive form of senile psychosis, that an affective disorder appearing in senescence is commonly the manifestation of some cerebral degenerative process. This is one of the sources of the widely prevalent view in contemporary clinical practice that there is a large group of cases in which dementia and a depressive (and less often a manic) symptom-complex are associated. The overlap being large, an ill-defined line of demarcation is held to exist in old age between the organic degenerative diseases and the affective illnesses of a “functional” kind.