Marine mammals, because they spend their entire lives in the sea without access to fresh water, present an interesting problem in regard to water equilibrium. It is to be expected that the need for conserving water would lead to noteworthy specializations, particularly in renal function, and the following data were collected in a preliminary survey of this problem in the common harbor heal, Phoca vitulina, Linnaeus. The observations concern the rate of urine formation; the osmotic pressure and nitrogenous composition of the urine ; the excretion of phosphate, chloride, sulphate, calcium and magnesium, and the simultaneous renal clearances of inulin and creatinine.
A young female seal weighing about 40 pounds, born in the spring of 1935, and supplied through the courtesy of the Boothbay Harbor Station of the U. S. Bureau of Fisheries,2 was kept in a floating trap tied alongside the laboratory wharf, from which the animal could be removed by a net when desired. During catheterization it was strapped on its back in a suitable holder. Urine was collected by catheter and blood by cardiac puncture, coagulation of the latter being prevented by heparin. The osmotic pressure of the urine was determined by Johlink ( '31) method, urea by Van Slyke's manometric method ( '27), and ammonia by Nesslerization after absorption on and re-extraction from permutit (Folin and Bell, '17). Total creatine was converted to creatinine A preliminary report on this work has been made in the bulletin of the Mount 'We wish to acknowledge our indebtedness to Mr. Thomas H. Dorr for his Desert Island Biological Laboratory, 1935. cooperation in procuring this animal. 465 'For method6 for the determination of inulin and creathine clearancee, and their significance, see Shannon ( '35).