AN ECONOMY OF WATER IN RENAL FUNCTION REFERABLE TO UREA

Abstract

The water requirements for the removal in urine of substances (the electrolytes Na, K, Cl, HCO3, H2PO4, and SO4, and the non-electrolytes urea and creatinine), which, taken together, constitute about 95% of the total materials presenting for excretion, were studied by placing relatively large amts. of the substances, singly and in mixtures, in the food of rats, and measuring their conc. in the urine. Water requirements for any mixture except one containing urea represented the sum of the requirements for the several components of the mixture; for a mixture containing urea, the water requirements were less than this sum. While no explanation of this apparent anomaly is offered, the fact that the largest "waste product" in urine incidentally performs an important service to the organism by conserving water (a conspicuous necessity for terrestrial animals) is an interesting instance of the fitness of biological substances.