Phosphate of lime occurs in the organism in two forms, viz., as the neutral or basic phosphate, 3CaO,P0, and the acid phosphate, The neutral phos phate occurs in all the solids and fluids of the body, but is most abundant in the bones, in which it amounts to about 57 per cent; and in the enamel of the teeth, in which it ranges from 80 to 90 per cent. It may at first sight appear inexplicable how a salt so perfectly insoluble in water as neutral phosphate of lime, can be held in solution in the animal fluids. In some fluids, as the blood, it is probably, in part at least, combined with albumen, with which it forms a soluble compound; while in other fluids, as the urine, it is held in solution by a free acid or by certain salts (as, for example, chloride of sodium), whose watery solutions are more or less able to dissolve it. if any proof is wanted of the functions of this salt in relation to the bones, it is afforded by the well known experiment of Chossat, who showed that when too small a quantity of it is taken with the food, the bones lose more or less of their hardness and firmness, and fractures do not readily unite. Phosphate of lime, like the phosphates of the alkalies, is indis pensable to cell-formation; and as a good illustration of this fact, it may be mentioned that in the mantle of the mollusks (where new cells for the formation of shell abound) this salt is far more abundant than in any other part of the body. Although by far the
greater quantity of the phosphate of lime found in the body has doubtless pm-existed in the food, yet it is unefuestionable, that a part of it is formed within the organism by the action of carbonate of lime on the phosphoric acid that is formed during the disimegra tion of the phosphorus-containing tissues, such as the brain, for example. . In man find carnivorous animals, a certain portion of the phosphate of lime is eliminated by the kid neys, and the rest is carried oft in the excrements; while in herbivorous animals tht whole is carried off in the excrements. The aciti phosphate of lime is occasionally found in the urine of man and carnivorous animals. but is of no practical importance. For a notice of the amount of earthy phosphates daily eliminated by the kidneys, the reader is referred to the article URINE.