The problem of absorption from the intestine has taken on a new significance since it has been appreciated that the failure of calcification in rickets is coincident with and apparently dependent on the absorption of minerals. The experiments of Schabad,1 Schloss2 and others, including us,3 have shown that active rickets is associated with defective absorption of calcium and phosphorus, and that as the disease heals, large quantities of these elements are retained. Moreover, it seems clear that the absorption of these elements can be increased in at least two ways: (1) by the administration of a factor contained in certain animal fats, of which cod liver oil is the best example; and (2) by the use of ultraviolet rays. Both of these measures are effective, even though the quantity of calcium and phosphorus supplied varies greatly. It has been supposed that these substances act by altering in