The disturbance of calcium and phosphorus metabolism in rickets is only partially reflected in the concentration of these substances in the serum; while a low phosphorus concentration is one of the most constant findings in the active stage of the disease, the concentration of calcium is, generally, either normal or only slightly decreased. There are, however, indications that this calcium level is rather precariously maintained. In infants with rickets, tetany with a low serum calcium occasionally develops, and in animals on a rachitic diet the sudden addition of vitamin D in some form may cause a catastrophal drop in the serum calcium.1 This instability of the calcium concentration in the serum of the rachitic individual is in marked contrast to the constancy of the serum calcium under normal conditions.
It will be shown in the present report that the serum calcium of the rachitic animal not only may be