Lv. the Biochemistry of Silicic Acid Vi. the Solution and Excretion of Silica

IN papers II and III of this series [1933, 1, 2] it was shown that the excretion of silicic acid in the urine could be influenced by the administration of silica. The urinary level was largely dependent on the amount of silica which was orally ingested, either as a constituent of the food, or as added mineral material. Both oral and parenteral administrations lead to prompt elimination inthe urine. Large amounts of silicic acid, given by continuous intravenous injection, were quickly excreted by the kidney. No marked increase in the silica content of the blood was observed, evenwhen the concentration in the urine was enormouslyincreased. Evidence was obtained that solution of silica dust may take place in the lung [King & Dolan, 1934]. Increased urinary excretion of silica in animals was obtained following administration by intratracheal insufflation, and in humans following dust exposure. This silicic acid arising from the solution of particles in the lung was presumably carried by the blood to the kidney where it was excreted. Some evidence was obtained that the urinary silica was at a higher level amongst gold miners than in a non-mining population, but the urinary silica values were found to be so dependent on the nature of the diet that no conclusions could be drawn in single cases [see also Goldwater, 1936]. Bloomfield et al. [1935], however, claimed to show a relation between the silica dust exposure of men in the anthracite coal industry and the amount of silica in the urine. The urinary excretion of abnormal amounts of silica cannot be taken as evidence of exposure to dust, but only as indicating an excessive intake of silica, either through ingestion or tbrough inhalation. In the present study an attempt is made to correlate the solution of various forms of silica in body fluids [King & McGeorge, 1938] with the urinary excretion of silicic acid following administration of the different forms of silica by the oral, intraperitoneal and in some cases the intratracheal route.