Experiments concerning the question of secretion of phenolsulphone-phthalein by the renal tubule

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Abstract
Phenol red, applied to the surface of a decapsulated rabbit''s kidney, passes into the urine eliminated by it. A similar result is obtained when the equivalent experiment is made with the frog''s kidney. When salt solution is made to flow from the ureter through the tubule to the capsule, during perfusion of the renal portal system with phenol-red solution, phenol red can be identified in the saline collected from the capsule. Complete obstruction of circulation through the glo-merulus does not prevent phenol red from entering the tubule and becoming concentrated there. When an excised frog''s kidney is immersed in oxygenated phenol red solution, the dye passes into the tubule and becomes concentrated. These facts, which present the appearance of secretion of phenol red by tubule cells, are best explained by assuming diffusion of water and dye into the tubule at one level, active extrusion of water and retention o dye at another, and a fluid current within the tubule from the one level to the other. The basis of fact in support of these assumptions is as follows: Cyanide, employed to abolish vitality of tubule cells, abolishes the power of the excised kidney to concentrate phenol red within its tubules. Cyanide does not prevent entrance of phenol red into the tubule of the excised kidney. Cyanide abolishes the power of the tubule to retain phenol red within it. Cyanide stops the fluid current within the tubule from one level to the other: the existence of such a current was demonstrated by injecting carbon or colloidal dye into the tubule and noting the progressive changes in its distribution New proof of re-absorption of water from the tubule is presented. The possibility of reinforcement of glomerular elimination by a process of diffusion into the tubules is suggested. Reasons are outlined for disagreeing with recent writers who have adopted the secretion theory in explanation of certain features in the renal behavior of phenol red.

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