. Kirkes' handbook of physiology . erum albuminis not excreted. These are both non-dialyzable compounds. Sugar andurea, both readily dialyzable, present the same comparison, , urea is ex-creted, while sugar is not. If, however, the percentage of sugar is high, cent or more, it is then eliminated. The excretion of the highly diffusiblesodium chloride bears a similar quantitative relation to excretion. If presentin the blood in relatively low amounts it is not secreted, while if the concentra-tion is slightly greater it may be quickly eliminated. Other inorganic salts,present only in
. Kirkes' handbook of physiology . erum albuminis not excreted. These are both non-dialyzable compounds. Sugar andurea, both readily dialyzable, present the same comparison, , urea is ex-creted, while sugar is not. If, however, the percentage of sugar is high, cent or more, it is then eliminated. The excretion of the highly diffusiblesodium chloride bears a similar quantitative relation to excretion. If presentin the blood in relatively low amounts it is not secreted, while if the concentra-tion is slightly greater it may be quickly eliminated. Other inorganic salts,present only in traces, are meanwhile rapidly eliminated. Even the rapidelimination of a slight excess of water in the blood can scarcely be explainedon purely physical grounds. To discharge the water across the glomerulusfrom the blood to the urine requires an expenditure of osmotic pressure muchgreater than that balanced by the blood pressure. That is, the epithelial cellsmust do work, and the energy is dependent on metabolism in the cells. At. Fig. 303.—Curve Taken by Renal Onkometer Compared with that of an Ordinary Blood-pressure Curve, a. Kidney curve; b. blood-pressure curve. (Roy.) least one substance, hippuric acid, is built up chemically by the renal cellsand secreted as such. It would seem, therefore, that the separation of urine in the kidney is asecretory process dependent on the protoplasmic activity of the living renalcells, that the apparent selective property of the cells is a manifestation ofsuch activity, and that even water is secreted. Diuretics. Certain substances increase the flow of urine and arecalled diuretics. They act directly on the renal epithelium, for example,urea, or indirectly on the circulatory system to increase the flow of is a well-known diuretic which increases the efficiency of the circula-tion. It also stimulates the renal epithelium with the production of a markedincrease in the flow of urine. Caffeine diuresis can best be explained
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