The citric acid content of animal tissues, with reference to its occurrence in bone and tumour

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Abstract
The citric acid content of the solid tissues of several spp. of animals was detd. The hard substance of bone contains a hitherto unsuspected store of citric acid, which may constitute some 70% of that contained in the whole body. The marrow and cartilage contain much smaller amts. Variations in the citrate content of bone, believed to be due to hormonal and dietary conditions, are reported. The variation of citrate greatly exceeds that of the other bone constituents, suggesting that the citrate is in a readily available form in vivo. In vitro it is not readily extracted from dried powdered bone by water, alc. or ether. Pure citric acid was isolated from dried bone meal, and pure pentabromo-acetone has been prepared from a trichloroacetic acid filtrate of bone meal in 80% of the yield calculated from analysis. The substance estimated in bone is in fact citric acid. The skin and hair have high contents of citric acid, which may arise, at least in part, from the sebaceous secretion: a high content was found in a human sebaceous cyst. The citrate present in hair is to a large extent extractable by water. The very young (3- to 5-day) chick embryo is rich in citric acid, and the amt. present is sufficient to combine with 1/3 of the total embryonic Ca. As development proceeds, Ca increases more rapidly than citrate. Tumor tissue usually, though not invariably, contains much citric acid. The need for revision of certain expts. on the citric acid balance in animals is pointed out. The existing hypotheses of "citrate-like substances" being concerned in Ca metabolism receive their main exptl. support from the present detection of citrate itself as a major constituent of bone.

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