Several types of operative damage to the pituitary body or to the tuber cinereum of the dog cause a polyuria which lasts about three days. A few observations of more enduring polyuria have been reported. In Crowe, Cushing and Homans's Obs. 34 (partial removal of the anterior lobe and separation of the stalk) the polyuria was still present when the animal was killed six months after operation. Camus and Roussy's dog “Moustachu” was putting out large amounts of urine when killed in the seventh month. Autopsy showed that the tuber cinereum had been punctured and that the stalk had been divided. Matthews twice produced polyuria by introducing through the sphenoid bone a piece of gutta-percha tissue which impinged on the posterior lobe, stalk and tuber cinereum. One experiment lasted nine weeks before the animal was killed. Camus and Roussy reported two dogs with “permanent diabetes insipidus” which were still alive ten and twelve months after the production of a lesion intended to involve only the tuber cinereum. Bailey and Bremer, who produced small lesions of the tuber cinereum, said that in three dogs “the polyuria was permanent.” The experiments lasted ten days, six weeks and four months respectively; in the third animal the posterior lobe had been detached from the infundibulum. The matter at issue is whether the polyuria is due to suppression of the secretion of the pars intermedia, or to injury of a hypothetical nerve center in the tuber cinereum, or to some other cause. The average length of life in the eight observations summarized above was five months. It has been assumed in some of these experiments that the polyuria was permanent. I have made observations which bear on the question of permanency. Dog 4; female, weight 6,135 gm., about 6 months old, had an average daily output of 140 C.C. of urine. Jan. 5, 1920, under ether anesthesia, the pituitary gland was exposed by Paulesco's technic, and an incision was made through the tuber cinereum which opened the third ventricle and completely separated the stalk and gland from the base of the brain. The output of urine rose for three days to about 600 c.c., dropped to 200 C.C. for the following four days, and rose to 1,000 c.c. on the ninth day. From that time until Apr.