At present, much attention is being directed to calcium in the diet. There are, of course, two main reasons for this emphasis on the part of students of nutrition: first, the usual American dietary has been shown to be less satisfactory in its content of this element than in most other aspects while, second, there is a relatively large demand for calcium in the body, especially at certain periods in the life cycle. The normal development of bones is conventionally associated with an adequate supply of lime. However, phosphorus is likewise fundamentally involved in skeletal growth, but, since it is more plentifully supplied in the ordinary dietary, it seems to have received somewhat less attention by investigators of the biochemistry and pathology of bone development. The fact that most rations provide a sufficient supply of phosphorus indicates the variety of chemical combinations, both organic and inorganic, in which this element