The Solubility of Calcium in Serum

It appears that about 20 per cent of the serum calcium is ionized (Neuhausen and Marshall, 1922), and that 60 or 70 per cent is diffusible (von Meysenbug, Pappenheimer, Zucker, and Murray, 1921). These figures show that serum calcium is not present in simple aqueous solution. Practically all blood calcium is found in the serum (Kramer and Tisdall, 1922). The normal value for adult humans is subject to variations between 9 and 10.5 mg. per 100 ml. of serum (Kramer, Tisdall, and Howland, 1921), and fhe value for other animals is abollt the same. A decrease to 7 mg. per cent or lower is suggestive of approaching tetany in parathyroidectomieed dogs (Salvesen, 1924). Hypercalcemia may also be induced in dogs by the action of parathyroid extract, with serious or fatal effects above 15 mg. per cent (C&p, Clark, and Scott, 1925). The highest values found by these authors were around 21 mg. per cent. Much higher values may be found aft,er injection of calcium salts; and by absorption of calcium salts from relatively strong solut,ions introduced into the intestine values as high as 35 my. per cent may be reached (unpublished data of the author). These examples show possibilities of considerable variation, and as the serum samples are centrifuged before determination it is probable that they represent figures for dissolved calcium. The literature does not suggest concomitant changes in the chemical characteristics of the blood sufficient to allow for such an increase in calcium solubility over the normal.