T W O FIGURES
Evidence for the use of inulin as a glomerular filtrate measuring substance has been gathered from a wide variety of vertebrates including the dogfish, teleost, bird, dog and man. (Review in Smith, Physiology of the Kidney, '37.) In the frog, Hendrix; Westfall and Richards ( '36) have shown that after intravenous inulin injection the glomerular urine contained the same concentration of inulin as the plasma. These were the results of microanalyses of fluids obtained directly from the exposed kidney of the frog. Also, Richards and his co-workers ('35) demonstrated in a double perfusion experiment that the frog's kidney was unable to excrete inulin when only the tubular blood supply contained inulin and that of the glomerulus did not.
Creatinine has been found to be handled in a variety of ways by the vertebrate kidneys. The clearance of exogenous creatinine was found to be identical with that of inulin in the dog by Shannon ('35 and '36), Richards, Westfall and Bott ( '36) and Van Slyke, Hiller and Miller ( '35), in the rabbit by Kaplan and Smith ( '37)' in the seal by Smith ('36), and in the sheep by Shannon ( '37). Clearances of exogenous creatinine exceed simultaneous inulin clearances in the dogfish (Shannon, '34), teleost (Pitts, '36), chicken (Shannon, '38), man (Shannon, '35), and several other primates (Smith and Clarke,