The tubules of the mammalian kidney, vitally stained with erythrolitmin, show a significant color pattern, the cells of certain regions appearing bright blue and others brilliant red. The dye is segregated within the cytoplasm, staining fine granules diffusely.

Under normal circumstances of renal function erythrolitmin is stored in the lining cells of the glomerulus and the epithelial cells of the proximal convoluted tubules in the blue, alkaline form. In the cells of the final portion of the distal convoluted tubules the dye is red. Between these regions a narrow transitional zone can be found, at times above, at times below the loop of Henle, in which the erythrolitmin-stained granules in the tubule cells are violet, or red and blue within the same cell.

Alterations in the relative reaction of certain regions of the tubules, as disclosed by the color of the dye within the cells, can be induced by means that alter the reaction of the urine. When acid urine is being secreted there is a change from relative alkalinity to acidity high up in the tubular canal, in the proximal convoluted tubules. During the secretion of markedly alkaline urine the intracellular granules appear blue most of the way down the tubular canal, even to the first portion of the distal convoluted tubules. When the urine is neutral the cells above the descending limb of the loop of Henle are alkaline to erythrolitmin, and those below this point appear acid.

The granules within the endothelial cells of the glomerulus and the epithelial cells of the first portion of the proximal convoluted tubules are always alkaline to erythrolitmin; while those within the cells of the final portion of the distal convoluted tubules are always acid regardless of the reaction of the urine. Only after complete suppression of urine as result of massive doses of acid do granules of the sort first mentioned manifest the color indicative of acidity.

The interpretation of the findings waits upon further work.

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