SECRETION OF INULIN, XYLOSE AND DYES AND ITS BEARING ON THE MANNER OF URINE-FORMATION BY THE KIDNEY OF THE CRAYFISH

Abstract

1. The techniques of measuring the rate of urinary flow and of collecting urine are described. The collection of urine from the nephropores by suction is a satisfactory procedure provided a correction is applied for the water lost by evaporation. 2. The techniques of collecting blood and of measuring renal clearances in the crayfish are described. 3. Raising the internal volume by one-third and therefore, presumably, augmenting the internal hydrostatic pressure, by the injection of 1 cc. of crayfish-saline, does not increase the rate of urinary flow. 4. Inulin and xylose will appear in the urine after being injected into the haemocoele. Glucose will occur in the urine provided enough is injected to permit its existence in the blood for a sufficient period. 5. The inulin-clearance and the U/P ratio of inulin vary inversely with the concentration of inulin in the blood. This demonstrates that inulin is secreted. 6. Inulin is not hydrolyzed by the hepatopancreas, kidneys, somatic muscles, or blood. 7. At low plasma-levels, the U/P ratios of xylose are very much below unity but rise above unity at high plasma-levels. This shows that xylose is either actively resorbed from a filtrate or is outwardly secreted but, with the low plasma-levels, at a relatively low rate compared with the secretion of water. The xylose-clearance: plasma-xylose curve is practically identical in shape with the U/P: plasma-xylose curve. 8. Although the renal clearances of xylose are much lower than the renal clearances of inulin, the plasma-concentration of the monosaccharide falls more rapidly than that of the polysaccharide. This may be partly because the tissues can destroy xylose. 9. Only the labyrinthic cells can accumulate and outwardly secrete cyanol, phenol red, indigo carmine, basic fuchsin, and acid fuchsin. The coelomosac, but not the labyrinth or tubule, can accumulate Congo red. These dyes cannot accumulate in, and apparently do not penetrate into, other tissues of the body. 10. Only the cells of the proximal half of the tubule accumulate methylene blue. 11. Colloidal carbon does not enter the kidney; this is functional proof of the absence of a nephrostome. 12. The cytoplasmic pH of the labyrinthic cells is about 7; the pH of the bladder-contained urine is about 7.5. 13. The available facts (histological, chemical, physiological, and phylogenetical) indicate that the nephron of the crayfish is primarily if not entirely an organ of outward secretion.