Two years ago we developed a special interest in diabetes insipidus,1 and as a result have been carrying out investigations on patients suffering from this disease. During the course of clinical studies certain observations were made which led to experiments in animals relative to water balance and to water intoxication. In this study we shall report (1) the results of our clinical studies in the fifteen cases of diabetes insipidus observed during the last two years in the Mayo Clinic and in

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... University Hospital, Minneapolis; (2) the effects on urinary secretion of the subcutaneous injections of the extract of the posterior lobe of the pituitary gland in normal dogs and in dogs which have undergone resection of the renal nerves ; and (3) the production of water intoxication by the administration of water by mouth subsequent to the subcutaneous administration of pituitary extract. STUDIES IN DIABETES INSIPIDUS 2 Etiology.\p=m-\We have made an attempt to determine the etiology of the diabetes insipidus in our cases. One patient had brain tumor, not definitely localized but known to be supratentorial ; another had a hypophyseal tumor, and four had syphilis ; in nine cases no causative factor could be determined. The incidence of syphilis in our series is high. Its etiologic importance has been emphasized by Fournier,3 Futcher,4 and Oppenheim.5 Whether or not syphilis was responsible for the diabetes insipidus in our cases could not be determined, but vigorous treatment for syphilis failed to exercise any significant effect on the course of the diabetes insipidus.