It may be considered an open question whether diabetes insipidus and diabetes mellitus represent different phases of the same disease, but their invariable consideration separately indicates that they are looked upon as independent affections. Nevertheless, it does not seem difficult to conceive that a lesion of certain extent or intensity might give rise to increased secretion of urine alone, and that the same lesion, though of greater extent or intensity, might give rise, additionally, to the presence of sugar in the urine, with the other attendant phenomena of saccharine diabetes. Instances of conversion of one form of diabetes into the other are rare, but a case has recently been placed on record by Blackett1 in which diabetes mellitus developed in the sequence of diabetes insipidus. The patient was a man, 54 years old, who had had a severe attack of influenza, had been overworked, had suffered a profound shock from