In 1915 McCollum and Davis published two papers which described a satisfactory method for interpreting such experiments. They gave two convincing demonstrations of the applicability of their theory of interpretation, which has formed the basis of all the more important nutrition studies since that time. One of these was a description of a successful growth experiment with young rats fed a diet consisting of purified protein, carbohydrate and mineral salts supplemented with such a fat as butter fat, together with an extract of a natural food which contained the anti-neuritic substance. The same diet without the extract proved a failure, as it also did when a vegetable fat or the body fat (lard) of animals replaced the butter fat. An adequate amount of fat was not the necessary-element, but rather the right kind of fat, or fat which contained in solution some substance which is essential for the normal functioning of the body. This experiment demonstrated also that a second substance, the anti-neuritic factor, was equally indispensable with the one furnished by butter fat. The second demonstration of the validity of the view which was expressed as to the essential components of a diet was made with polished rice. It was clearly shown that in order to make this degermi-nated and decorticated food grain complete from the dietetic standpoint it was essential to supplement it with a protein to make good the shortage of this factor; with certain mineral salts, and with a growth-promoting fat and an extract which furnished the anti-neuritic substance.