A third model illustrating some phases of kidney secretion

Abstract

Abstract The question is raised of the mechanism by which water is secreted by such a secreting parenchyma as a kidney. The experimental evidence is reviewed which indicates that only free water can be separated from the blood and that the separation of such water costs the kidney no work. This supports the conclusion that such separation is a mere filtration process, and since the secreting parenchyma of such an organ as the kidney is a hydrated colloid which has properties closely akin to a solid hydrated soap, the filtration properties of such a soap (sodium stearate) are studied to see whether any analogy exists between its behavior and what may be observed biologically. 1.1. Hydrated sodium stearate allows water to pass through it under slight hydrostatic pressure, the ease of such passage being increased as the concentration of the hydrated colloid is lowered. 2.2. While free water passes readily through such a hydrated colloid, water tied to a hydratable colloid (liquid sodium oleate) can not. 3.3. Salt solutions lead to a greater filtration of water than plain water and this (a) according to their concentration and (b) their kind, generally speaking. The higher the concentration of any salt, the greater the filtration of water. On the other hand, at given concentration, salts of ammonium or potassium produce less filtration than salts of sodium, and these less than those of magnesium or calcium. The findings on soaps are here identical with the behavior of these same salts upon the living organism. When, however, the effects of equally concentrated salts with the same basic radical but different acid radicals are compared, no such diuretic differences appear as occur in living animals. 4.4. The theory of the action of these effects is discussed, it being pointed out that because of the existent differences in chemical composition of fatty acids and of the polymerized amino acids known as protein it is possible in the former to produce only one series of salts as different bases are introduced into the fatty acid. In the case of the proteins a similar series may be produced, but because of the existence in the latter of NH 2 groups, a second series may be produced through the linking of acid with these groups. Colloid-chemical and physiologic behavior are then an expression of the solvation and solubility properties of the different compounds thus formed. 5.5. The dangers of applying without due reserve indicator methods and the laws of dilute solutions of electrolytic dissociation, etc., to the normal cells and fluids of the body but not to their secretions is reemphasized.