Rehberg proposes that formulation of Cushny''s filtration-reabsorption theory is at fault in distinguishing between threshold and no-threshold bodies. All substances except creatinine behave like threshold bodies. Rehberg studies creatinine in human blood and urine and calculates degree of concentration in kidney. The amount of glbmerular filtrate and of reabsorption is calculated from formulae:[image] where: A = substance filtered, F = amount filtrate formed in capsules, U = amount of urine, Ap % = %A in plasma in diffusible state (by analysis), Au% = % A in urine (by analysis), C = Au%/Ap% = index of concentration, R= amount of fluid reabsorbed. Creatinine is studied because ingested creatinine is concentrated by the kidney to far greater extent than any other hitherto observed substance in the urine. In man after ingestion of 5 gm. creatinine and 200 cc. H2O, with 300 cc. H2O shortly after, blood and urine analyses are made (Folin methods, Leitz-Burker colorimeter). The amount of creatinine filtered indicates filtration from 200 cc. plasma per min. Rehberg maintains the possibility of driving this volume through tubules. If number of glomeruli at minimum is 2 million (Vimtrup), maximum filtration would be 0.1 cu. mm. per min. per glomerulus. Observed filtration is only 0.1 or 0.01 cu. mm. per same. If lumen of prox. convoluted tubules is 20[mu] diameter and 14 mm. length (Peter), 32 mm. Hg pressure is necessary. If reduction of volume by reabsorption occurs here, blood pressure is sufficient driving force for entire process. Rehberg maintains that blood flow is adequate to supply the needed volume on the basis of Vimtrup''s demonstration that inner epithelium of capsule follows each glomerular capillary like the finger of a glove so that filtration is only through a single delicate membrane composed of capillary endothelium and capsule endothelium. Vimtrup estimates minimum surface of glomerulus at 442,000 sq. [mu], for 2 million glomeruli =8800 sq. cm., so 200 cc. would filter at rate of 4[mu] per sec. Quantity of fluid reabsorbed (50-200 cc. per min.) is like similar absorption in bird cloaca per surface (surface of human prox. convoluted tubules estimated from above data [minima], 17,600 sq. cm.). Rehberg points out that diuresis under Cushny''s theory may result from (1) number of units operating (increased by opening blood flow through previously unused glomeruli), (2) filtration through open glomeruli increased, (3) filtration unchanged but reabsorption less.