The dimensions of the renal tubules of Necturus maculosus

Abstract The method of micro‐injection was used in the study of a large number of tubules. The limits of the several parts of the tubule were determined with a high degree of accuracy without sectioning; the error of the measurements was small. Of 137 tubules studied the measurements of forty‐nine comprised the entire length from renal corpuscle to collecting duct or ureter. The proximal tubule was found to be about twice as long as the distal. While the longest proximal tubule was nearly six times the length of the shortest, the great majority of tubules fell within a much shorter range. There was little or no correlation between proximal tubule length and weight of the animal. The proximal tubule is larger in diameter than the distal tubule. Calculations indicate that the area of exposed cell surface in the proximal tubule is nearly four times as great as in the distal; however, compared to tubule volume, a relatively greater cell surface is exposed in the distal tubule.