THE RELATION OF PARTICLE SIZE TO MECHANISM OF DYE EXCRETION BY THE KIDNEY

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Abstract
A correlation of the degree of filter-ability of certain dyes through standard collodion membranes with the mechanism of their elimination, whether glomerular or tubular, by the perfused frog''s kidney suggests that the method of their excretion is determined by the size of the dye particle. Easily filterable dyes of small particle size, such as phenol red and indigo carmine, passed readily through the glomerular membrane when the dye was led to the kidney by way of the renal artery. Dyes of moderate particle size and therefore less filterable, such as neutral red, required tubular activity for their elimination, and were therefore excreted more efficiently when introduced into the perfused kidney by way of the renal portal vein. Dyes whose particles were so large as to be unfilterable were not excreted by the perfused kidney. The special cases of trypan blue and neutral red elimination confirmed this hypothesis. The former, consisting of a pink and a blue element, one filterable and the other unfilterable, was separated in the same manner by both ultra-filtration and by excretion through the kidney into its two components. With neutral red, the dye particle size was demonstrated by both ultramicroscopic observation as well as by ultrafiltration to decrease markedly in size with increase in the hydrogen ion concentration of the solution. Whereas the alkaline form of the neutral red with its larger particles was eliminated, as stated above, by the tubules of the perfused kidney, this acid form of the dye with its small particle size was eliminated through the glomeruli. The relation of these findings to conflicting recent literature is discussed.

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