Calcium and Inorganic Phosphorus in the Blood

By a systematic study of the blood of normal rabbits (1), it was found that both the absolute and relative amounts of calcium and inorganic phosphorus exhibited periodic variations and that, among animals living in the laboratory, there was evidence of a tendency toward a progressive increase in calcium and of a decided decrease in inorganic phosphorus of uncertain duration and extent. I t appeared that, while a number of factors may have contributed to the production of the variations noted, one of the chief causes was the occurrence of changes in the light environment. I t is, of course, well known that ultra-violet radiations of short wave-length (3100 .~gstr6m units or less) are capable of exerting a profound influence on the inorganic phosphorus content of the blood and hence on the caicium-phosphorus equilibrium. In the present instance, however, it was evident that the variations found among animals living in the laboratory could not be attributed to the action of ultra-violet light of short wave-length as the light received by these animals was filtered through glass. From previous experiments (2), it had been found that rabbits living under similar conditions showed periodic variations in the weights of organs, or organic constitution, and in their reaction or susceptibility to disease, and that these conditions were subject to the influence of a light environment which included no ultra-violet of short wave-length. I t seemed probable, therefore, that blood calcium and inorganic phosphorus might be influenced by similar