PHOSPHATES (in physiology). The following phosphates* play an active part in the chemistry of the animal body.
Phosphate of soda, which may occur under any one of the three forms 3NaO,P0, m or All these salts are soluble in %rater; and the first two have an alkaline reaction, while the third is acid. By exposure, of the second of them salts (2Na0.110,P0,) to a red heat, it is converted into what is termed pyrophosphate of soda (2NaO,P00, in which the phosphoric acid is obviously no longer tribastc, but bihasie; and by similarly treating the third of these salts we convert it into the so-called inetaphosphate of soda (NaO,P00, in which the phosphoric acid is monobasic. It is in consequence of these changes under the action of heat, that the terms pi/cop/we/Aerie and metaphosphoric have been used as synonyms for Libasic and inonahasic phosphoric acids. Phosphate of soda, in one or other of the above forms, occurs as a constituent of all the animal fluids and soft tissues of the body, but is especially abundant in the urine and the bile. There are reasons for believing that it is the second and third of these salts which occur as constituents of the animal body, although the first may possibly sometimes be found. Pyrophosphate and metaplmsphate of soda are often found in the ashes of animal fluids or tissues after the process of incin eration, but they merely result from the action of heat on the two other salts. The fol lowing remarks on the derivation, elimination, and physiological importance of the phos phate of soda, are equally applicable to the corresponding salts of potash, which are always associated with them. The phosphates of the alkalies, which occur in the animal body, obviously owe their origin, either directly or indirectly, to the food; viz., directly, by being ingested as phosphates of the alkalies; or indhicetly (within the system, by the action of phosphate of lime on salts of the alkalies. The elimination of these salts from the system is necessary, because they are being constantly supplied by the food; and this process is effected mainly by the kidneys and the intestinal canal. In the carniv orous animals, whose blood is much richer in phosphates than that of herhivora (the ash of the blood of the dog, for example, contains from 12 to 14 per cent of phosphoric acid, while that of the ox or sheep does not contain more than from 4 to 6), these salts tire carried off by the urine; but in consequence of the formation of free acids as pro ducts of the disintegration of the tissues, a portion of the base is abstracted from the originally alkaline phosphates, and corresponding portion of acid is liberated.
originally alkaline stilt is thus rendered neutral or even acid; and the occurrence of •The means of distinguishing between the 'tilts of tribasic, bibasic, and monobasic phosphoric acid, are given in the article Pkiostmones.
the acid phosphate of soda, Na0,2HO,P05, in the urine is thus explained. In the herbivorous animals, on the other hand, the urine contains no phosphates, the whole of the phosphoric acid taken in their food being eliminated by the intestinal canal in the form of the insoluble phosphates of lime and magnesia. Although the general distribu tion of the phosphates of the alkalies in the nutrient fluids (there is forty per cent of them in the ash of the blood-cells; 28.4 per cent of phosphoric acid and 23.5 of potash in the ash ot cow's milk; and about 70 per cent of phosphoric acid in the ash of the yell of egg) is in itself an indication of their importance, the exact nature of their functions is not completely understood. Liebig has specially drawn attention to the peculiar grouping of the acid and alkaline fluids of the animal body. The permanence of this grouping is chiefly maintained, especially in herbivorous animals, by the conver sion, within the body, of alkaline and neutral phosphates into acid phosphates by the means already described. all tissue-forming substances (the protein bodies) are so closely connected with phosphates, that they remain associated during the solu tion and of these substances; and the ash of developed tissues (such as muscle, lung, liver, etc.) always affords evidence that acid phosphates existed in the recent tissue; and, further, no exudation froit the blood-vessels can undergo trans. formation into cells and fibers, or, in other words, become organized, unless, in addition to other condititions, phosphates are also present. Another very proof of the share taken by the phosphates in the formation and functions of the tissue, is the fact that, although herbivorous animals take up a very small quantity of phosphates iu their food, and although their blood is very poor in these salts, their tissues contain as large a proportion of phosphates as the corresponding parts of carnivora. Lastly, the fact, that one equivalent of the alkaline phosphate of soda possesses the property of absorbing as much carbonic acid as two equivalents of carbonate of soda, leads us to the belief, flint the power of attracting carbonic acid, which the serum of the blood pos sesses, is due at least as much to the phosphate as to elle carbonate of soda, and that, consequently, phosphate of soda plays RD important part in the respiratory process.