Abstract
1. 1. The concentrations of urea and ammonia in blood or serum and urine of frogs, Rana pipiens, were determined after 6–48 hr of mild dehydration in air. Increased concentrations of urea were observed in blood or serum of frogs dehydrated less than 12.5 hr in the spring-summer, but not in the fall-winter. 2. 2. Ammonia represented only 0.6–3.4 per cent of amino nitrogen excreted in the forms of ammonia and urea. Ammonia was not detected in serum during any season, but was present in blood that was hemolyzed. 3. 3. Administration of Pitressin did not alter the concentration of urea in serum of tap water treated frogs, except at high doses, where it was observed to cause a decrease in the concentration of urea in serum. 4. 4. The increase in serum urea levels was associated with an increase in urea production. The seasonal nature of this response is discussed.
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