Abstract
Although silicic acid has long been known to occur in practically every tissue of the living organism there has been no evidence that it is in combination with organic matter as are, for example, sulphuric and phosphoric acids. Drechsel 1 long ago reported its occurrence as an ester of cholesterol in bird feathers but there has been no confirmation of his observation since.
Kraut 2 has recently reported that the silicic acid content of human blood is constant in any one individual at different times, that it varies considerably in different individuals and that a temporary variation can be brought about in any one individual by the administration of silicates.
By the electro-dialysis of gelatin, ox tendon, horse and ox-blood, and human urine, the writer has recovered, at the cathode, small amounts of a jelly-like substance, containing both silicic acid and organic matter, and giving a test for carbohydrates. This substance is insoluble 20 in water, in 5% hydrochloric acid and in dilute alkali. It chars when heated on platinum and discolors concentrated sulphuric acid when heated. A suspension in water slowly gives the Molisch test for carbohydrates. It is changed by heating with 10% sodium hydroxide so that the organic matter and a part of the silicic acid go into solution, while the residue now left is soluble in 5% hydrochloric acid and contains calcium, iron and silicic acid. It does not give a test for cholesterol.
The organic fraction of the substance appears to be comparatively small and it cannot be stated to what extent a more complex substance was disintegrated by the electro-dialysis.
Unlike the present substance, colloidal silica is negatively charged and migrates to the anode.
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