Calcium and Phosphorus Studies in the Chick*

The majority of the published data dealing with blood calcium and phosphorus changes in rickets is based upon blood determinations made after the appearance of rickets. Values obtained after the symptoms of rickets are evident do not show when t,he reduction in the calcium and phosphorus first t.akes place. A true understanding of the relation of vitamin D t,o these blood changes can be obtained only if the analyses are made at frequent intervals. It is the purpose of this paper to show the changes in the calcium and phosphorus content of the blood and t.he ash content of the bone of chicks during the first 6 weeks of life when reared on rachitic rations and on the same rations plus vitamin D. The chick was used as the experimental animal for several reasons. Owing to the high vitamin D requirement of this species, the development of rickets takes place very rapidly on a diet of natural food materials without resorting to a distorted calciumphosphorus ratio. A sufficient quantity of blood for analysis could be obtained from one animal which eliminated the necessit,y of pooling the blood from several individuals. A sufficient number of animals could be placed on each ration to allow several determinations during the 6 week period. St.eenbock, Hart, ,Jones, and Black (I), Ackerson, Blish, and Mussehl (2), and Hughes and Titus (3) were the first workers to report low inorganic phosphorus and calcium in the blood serum