The biochemistry of silicic acid

Abstract

I. A colorimetric method (described) makes use of the blue color produced when silicomolybdic acid is reduced by 1:2:4-aminonaphthol-sulphonic acid. The phosphate is precipitated with CaCla and NH40H. Fe is removed as ferric phosphate in the presence of CaCO3. The blood is deproteinized by basic ferric acetate. The procedure was adapted to urine, blood, kidney and lung tissues.[long dash]II. All fetal tissues examined (human lung, liver, kidney, spleen, heart and brain, calf lung, kidney, liver, spleen and muscle, whole mouse) contain silica. The lung tissue of the adult contains the highest % of silica, while the blood contains only very small amts. The kidneys excrete silicate and the silicate output is higher for herbivora than for carnivora. The diet markedly influences the amt. of silica.[long dash]III. If either soluble or finely powdered silica was introduced in dogs by stomach tube, there was an increase in the output in the urine without a corresponding increase in the blood. A glycol ester of silicic acid intraven. injected caused a slight rise of silica in the blood and a marked rise in the urine. The blood appears capable of maintaining a much higher cone, of organic than of inorganic silicate. A suspension of finely divided silica intraven. injected killed a dog within a few hrs. The organic silicate killed 2 dogs in 5 days. Spraying of silicic acid into the lungs led to increased urinary output, but it is not certain that this was due to absorption from the lungs. It is suggested that animals possess a very low renal threshold for silicate.[long dash]IV. The addition of silicate to a culture soln. containing an abundance of nutrient salts caused increased diatom growth if the silica content was less than 100 mgm. per liter. In amts. above this, there seemed to be inhibitory effect. The dissolution of silica was more rapid in an autolyzing suspension of diatoms containing chloroform than in one that had been boiled. The unboiled portion of the diatom suspension was invariably dissolved more rapidly than that which was boiled.