Abstract
At intervals throughout the past year, with the exception of the summer months, we had occasion to make a considerable number of determinations of the inorganic calcium and phosphorus content of normal rabbits'sera. The results are of interest in that they reveal certain progressive variations due apparently to seasonal changes in the environment, and they also show an effect of caging that should be taken into account.
As received from various dealers, 144 male rabbits showed a blood calcium level of 12.31 mg. per 100 cc. of serum. 1 This general average was obtained, however, from figures that varied considerably for different months of the year, (Table I.) From a low level of 11.74 mg. in January, high levels were reached in May and November of 12.92 and 12.88 mg. Similar variations were found in the blood calcium level of 82 normal rabbits (110 determinations) which had been caged, individually, indoors in a well lighted and ventilated room, and fed hay, oats and cabbage for periods of 1 to 7 weeks. The figures for these rabbits parallel those obtained on admission, but show the blood calcium to be at a uniformly higher level—13.12 mg. per 100 cc. serum—with the January low level at 12.40 mg., and the May and November peaks at 13.62 and 13.47 mg. respectively. We have already noted 2 that the caging of normal rabbits, under conditions that obtain with us, results in a definite rise in the blood calcium. It remains to be seen how the apparent seasonal variations in the blood calcium can be correlated with the changes in the size and functional activity of certain elements in the endocrine system which Drs. Brown, Pearce and Van Allen have observed at the same seasons of the year. 3
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