The statement is, I think, also warranted that there is a considerable difference of opinion as to the classification of the different forms of manic-depressive insanity and that diagnostic procedure is far from being standardized. Many of these discrepancies are doubtless due to difficulties in differentiating between certain cases of manic-depressive psychoses and dementia praecox. The hospitals reporting lower percentages of the former usually show a much higher rate of the latter. Certainly there is room for an honest difference of opinion in many instances. It must be admitted, moreover, that our fundamental conceptions of these two great groups do not permit of a hard and fast line of demarcation between them in all cases. CHAPTER XII INVOLUTION MELANCHOLIA In 1896 Kraepelin first definitely outlined his views on dementia praecox, to which he assigned hebephrenia, although he did not at the time include katatonia in his delimitation of that disease. He also described melancholia in his fifth edition, classifying it as an involutional or retrograde presenile process (Das Irresein des Rückbildungsalters). He had not as yet formulated his theory of the manic-depressive psychoses although he described manic and depressive forms of periodical constitutional disorders. In 1899 he discarded the mania and melancholia of other writers altogether or rather included them in his new manic-depressive group, but still retained melancholia as a distinct entity occurring in the involutional period of life only. As has already been shown, melancholia is a term which had been used for centuries and in a general way applied to depressions of any and all types. Kraepelin's manic-depressive psychoses and dementia praecox very largely destroyed the integrity of this old-time conception. It has been shown, furthermore, that depressive states often constitute an integral part of the picture of general paresis. Symptomatic depressions more or less distinct in character have been associated with a number of somatic diseases. Senile psychoses, epilepsy, various organic conditions, the psychoneuroses and the psychopathic personalities have depressive manifestations well recognized and readily classifiable.