[NICHOLLS] CALCIUM CONTENT OF THE BLOOD 87 
from the mother’s food. The functions of gestation and lactation put 
a great strain upon the maternal organism in many ways and not least 
in their demand for lime. As an illustration of this we may cite the 
disease known as osteomalacia, in which there is a rapid and progressive 
diminution in the amount of mineral matter in the bones, which conse- 
quently become soft, brittle or pliable. This disease is almost confined 
to the female sex and is particularly apt to develop during pregnancy 
or shortly after. The relationship of the sexual organs to calcium 
metabolism will be referred to again. 
The amount of calcium existing in solution in the blood is very 
small, and in what form it circulates, whether phosphate or carbonate, 
or both, we do not certainly know. The amount, indeed, is so trifling 
that there is some ground for thinking, as some recent work would in- 
dicate,' that it may be present in the form of ions in combination with 
some of the proteins. Probably it exists in a dissociable and ionizable 
form and in a non-dissociable state as well. The amount, estimated as 
calcium oxalate, is given by Blair Bell as 0.025 to 0.02 per cent by 
weight. Considerable variation is found, however, in this regard in the 
different animal species. The blood of the rabbit, for example, con- 
tains about ten times as much calcium as does that of the dog. The 
amount in an ordinary state of health would appear to be fairly constant, 
with one or two exceptions. Bell and Hick” have shown that there 
is a marked rise in the calcium index during the later months of preg- 
nancy and a marked fall during menstruation, in the latter case being 
apparently correlated to a considerable excess of lime in the menstrual 
blood. 
The excretion of calcium from the body has been but little studied. 
Only a small proportion (about 5 to 15 per cent) of the total amount 
absorbed from the intestines is discharged in the urine. The bile is 
known to contain lime salts (chiefly phosphate), and it is probable that 
the larger part is eliminated by the intestinal mucosa and through the 
liver. The amount discharged by the urine is increased in osteomalacia, 
tuberculosis, and conditions of inanition. 
There are two periods of life in which the calcium metabolism of 
the body is of special importance, childhood and old age. During 
infancy and adolescence there is a constant demand for lime salts to 
build up the growing bone, and after middle life retrogressive changes 
begin to manifest themselves as evidenced by the increasing lightness of 
the skeleton, and the deposit of lime in situations where it formerly was 
not present or only present in trifling amounts, such as the costal 



1 Robertson, Journ. of Biol. Chem., 2; 1907; 317. 
2? Bell and Hick, Brit. Med. Journ. 1; 1909; 592. 
