During routine blood and urine studies on dogs which were being given daily injections of extracts containing the growth promoting principle of the anterior hypophysis, it was noted that some of the extracts exerted a marked diuretic action. In one dog weighing 18 Kg., the twenty-four hour urine output during the control period was approximately 750 cc. When injections were begun, the output rose to 7,300 cc. in the second twenty-four hour period and remained above 5,000 cc. for a week of observation. The daily output in another animal rose from an average of 800 cc. to 3,000 cc. Several other instances of this effect were encountered incidental to other observations.
I was impressed with this extreme diuretic effect, and experiments were planned under conditions more suitable for the study of water metabolism, in which the twenty-four hour water intake and urine output were accurately measured, and the specific gravity