Howland and Kramer (22) have recently reported studies on the composition of the blood with respect to phosphorus in normal and in rachitic children which are of great interest in this connection. Whereas the content of calcium in the blood remains markedly constant in health and in most diseases, the phosphorus may vary greatly. The blood of children contains 10-11 mgm. of calcium per 100 c.c. of serum. It falls below this level only in tetany, which condition is apparently directly brought about by the reduction of the calcium content of the body fluids. The serum of adults contains 9-10.5 mgm. of calcium per 100 c.c. The red corpuscles contain no calcium (22).

The inorganic phosphorus content of normal blood of children is, according to Howland and Kramer, about 5.4 mgm. per 100 c.c. of serum. The serum of adults contains but 2.1 mgm. of inorganic phosphorus per 100 c.c. In rachitic children the inorganic phosphorus content of the serum may fall as low as 0.8-2.9 mgm. per 100 c.c. of serum. It is remarkable that on the administration of cod liver oil to such children the inorganic phosphorus content of the serum at once rises to the normal or above. It is highly suggestive that the heightened concentration of phosphorus in the serum may be the cause of the resumption of deposition of calcium phosphate in the bones in rickets. There can no longer be any doubt that cod liver oil possesses a pronounced therapeutic value in the treatment of rickets, both in human and animal subjects.