METHODS

Simultaneous endogenous" creatinine," inulin and p-aminohippurate, free and total (free plus conjugated), clearances were determined in 18 normal male subjects during four to six hour periods throughout 24 to 48 hours. The subjects were all convalescent patients without clinical evidence of cardiovascular-renal disease. They were maintained at bed rest for at least 24 hours prior to as well as during the period of observation. They were on routine ward diets and were allowed fluids ad lib. The test substances were delivered by means of a con-stant delivery pump at rates varying from 0.20 to 0.50 cc./min. in 14 of the subjects. For the first three a pusher type pump was used in which the plunger of a 100 cc. syringe, filled withthe sustaining infusion, was slowly driven forward by a synchronized motor through a geared-down worm-screw drive. When empty the syringe