The most interesting point in the physiological action of lime salts is their influence on nutrition, the necessity of phosphate for healthy growth, whether vegetable or animal, being especially evident. Experiments with plants have shown that the phosphates are in close relation with the nitrogenous elements. If, for instance, the nitrogenous husk or coating of a seed be removed, the phosphates are removed with it, and in the starchy part of the grain none are found. In the leaves they occur in the parenchyma, not in the nervules, and generally are most abundant in the cellular parts of vegetables wherein nutrition and reproduction are most active (Liebig). Wheat, planted in earth containing phosphates, germinates and thrives, but if all phosphate of lime be removed, it germinates, indeed, but soon dies. Peas (which contain a larger proportion of azotized matter), when similarly treated, germinate and even bear a crop, but if this crop be sown in a soil without phosphates, it does not flower (Georges Ville: Conferences, Paris, 1865, Rabuteau). That the improvement in nutrition is not due to the presence or absence of phosphorus as such, but to phosphate of lime, is shown by experiments on birds. Wheat contains a large quantity of phosphate of potash, and when pigeons are fed upon this alone, and are prevented from getting any carbonate or other salts of lime, they waste away, and their bones become weak and brittle. If, on the other hand, they can obtain lime in any form, it becomes changed into a chloride during digestion, and combining with the alkaline phosphates of wheat, provides them with lime phosphates, and secures or favors their due nutrition (Chossat).

There is also evidence that lime phosphates serve especially to nourish cartilage, bone, tendon, and muscle, so that they have been fairly called "restorative or analeptic tonics" to the locomotor organs, as iron is to the blood, or phosphorus to the nerve-tissue. Thus, as the result of observations on the reproduction of the shell in crabs, Schmidt found that a combination of phosphate of lime and albuminous material was most favorable for the formation of osteoid cells; phosphate was required for the first growth, though carbonate was formed later. Mr. Bridgman noted the formation of "artificial cartilage" by the passage of an electrical current through a viscous solution of carbonate of lime (Hughes Bennett: Lancet, i., 1863, p. 5). Beneke found that phosphate of lime was specially abundant in plastic exudations and wherever new growth was going on, and he adopted the microscope as a ready means of its detection - for if a drop of sulphuric acid be added to the liquid, crystals of lime sulphate are very quickly formed (Lancet, i., 1851, p. 432). The organism can assimilate phosphate of lime either in the soluble acid form (for the liquids and soft tissues), or to some extent in the basic insoluble form (for the skeleton); but its effects are produced slowly, and without the evident stimulation which we associate with the action of wine, iron, or quinine, so that we describe such lime compounds rather as restoratives than as general tonics, and as modifying rather than stimulating nutrition. (As a readily noticed, though slight evidence, of the effect of lime phosphates on nutrition, Rabuteau notes that white spots on the nails often disappear under their use.)

Besides their effects on ossification, etc., M. Mouries, a distinguished chemist, has described a special effect of lime salts upon "irritability," or vital organic changes, so that if these salts are absent, assimilation and nutrition do not go on, and emaciation and death ensue, while if they are simply deficient, various degrees of lymphatic and osseous disease are produced. He has calculated especially that the food of those who live in towns is deficient in these principles, and that while every one ought to have at least 90 gr. daily, many, women especially, receive only about half that quantity; hence a secretion of poor milk and consequent weakly children, and he claims that by the use of a certain food containing lime phosphate with albumen, the proportion of still-born and of rachitic children in many families has been markedly reduced (quoted by Trousseau).

Any difference in the amount of urea and carbonic acid excreted under the influence of phosphate of lime is not exactly ascertained. The chloride of calcium is said to increase the amount of urine (Giacomini); and it is probable that like other chlorides it increases the excretion of urea (Rabuteau).