Untitled

Abstract

IN spite of the important role played by the kidney in the maintenance of the acid-base equilibrium of the body by eliminating a more or less acid urine, the mechanism, and especially the site of the acidification of urine, is still a matter of discussion. There seems to be general consent that the preliminary urine filtered off into the glomerular capsule is alkaline, of the same pH as the blood plasma. This was observed in the living frog by three different investigators using three different methods: microscopically, using phenol-red as indicator, by Bieter and Hirschfelder [1922, 1924]; by estimation of the pH of the glomerular punctate, by Wearn and Richards [1924]; and with the intravital microscope, using the tint of the fluorescence of fluorescein as indicator, by Ellinger and Hirt [1929 b, 1930 a]. The experiments were confirmed by Montgomery [1935] and by Ellinger [1934 a, 1940] and extended with similar results to the glomerular filtrate of the rat's kidney by Ellinger [1934 b, 1940]. In the experiments of Ellinger and Hirt [1929 b] it was further observed that in German R. esculenta in summer the preliminary urine was acidified to a certain degree in the proximal tubules and became still more acid during its passage through the lower urinary tract, especially in the distal tubules. In the same species in winter, urine was found to be far less acid [Ellinger and Hirt, 1930 a]. No acidification occurred in the proximal tubules and only slight acidification in the distal and collecting tubules. At the time when this work was done photography of the intravital microscopic pictures was not possible, as photographic emulsions were too inefficient as regards the speed and sensitiveness in the yellow and green. Ellinger and Hirt [1929 b, 1930 a] had, therefore, to rely on visual observations; and the colour tints of the intravital microscopic pictures could only be reproduced by colour drawings made with a camera lucida. Almost simultaneously Richards [1929] reported that phenol-red introduced directly into the lumen of the frog's tubule changed from red to yellow only in the distal third of the tubules. In 1934-1937 Ellinger [1934 a, b, 1940] repeated the intravital microscopic investigations in this country at different seasons of the year with Hungarian R. esculenta, and extended the observations to