NaH_{2}PO_{4} + NaCl = Na_{2}HPO_{4} + HCl. It is also to be noted that the disodium hydrogen phosphate, may, likewise, give rise to hydrochloric acid through its action on calcium chloride, as indicated by the following equation: 2Na_{2}HPO_{4} + 3CaCl_{2} = Ca_{3}(PO_{4})_{2} + 4NaCl + 2HCl. It is thus evident that hydrochloric acid may originate in the inter-reaction of these several salts which are known to be present in the blood; but obviously, the above reactions cannot take place in the blood itself, and we must look to the selective power of the epithelial cells of the gastric glands, as suggested by Gamgee,[96] for the withdrawal of the needed salts from the blood. Once present in the acid-forming cells, and perhaps aided by the inherent qualities of the protoplasm, the necessary chemical reactions may be assumed to take place, after which the newly formed acid may pass from the gland-cells into the secretion of the gland. [96] Physiological Chemistry of the Animal Body, vol. 2, p. 113. A later theory regarding the formation of the acid of the gastric juice emanates from Liebermann.[97] This investigator claims the existence in the mucous membrane of the stomach of an acid-reacting, nuclein-like body, which is apparently a combination of the phosphorized substance lecithin with a proteid. To this compound body Liebermann gives the name of lecithalbumin. It is apparently located in the nuclei of the gastric cells, is strongly acid in reaction, and, according to Liebermann, is an important agent in the production of the free hydrochloric acid of the gastric juice, although its action is somewhat indirect. According to this theory, the free acid is formed in the mucous membrane of the stomach from sodium chloride, through the dissociating action of the carbonic acid coming from normal oxidation. The thus-formed acid then diffuses in both directions, viz., through the lumen of the gland into the stomach-cavity, and in part in the opposite direction into the veins and lymphatics. It is the assumed function of the lecithalbumin to react with the alkaline sodium carbonate, produced simultaneously with the hydrochloric acid. This naturally gives rise to the liberation of carbonic acid and to the formation of a non-diffusible sodium-lecithalbumin compound, which is retained for the time being in the body of the cell. When the circulation of the blood, accelerated by the digestive process, returns to its ordinary pace, this latter compound is slowly decomposed by the carbonic acid with formation of the readily diffusible sodium carbonate, which passes into the blood-current. The rate of this latter reaction is impeded, or, perhaps regulated, by the swelling up of the lecithalbumin-containing cells, thus rendering the imbibition of the carbonic acid a slow process. The rate of production of the hydrochloric acid by this hypothetical process depends primarily upon the blood supply, and the oxidative changes by which carbonic acid is