The experiments of one investigator, Hopkins (3), were of a different type from those mentioned in the preceding paragraph. He met with complete failure in his attempts to nourish young animals on purified protein, carbohydrates, fats and mineral salts, but was able to induce growth with the same diet supplemented with small additions of milk. The milk furnished some substance or substances which were not present in the mixture of purified food substances, and which were essential for growth or the maintenance of health. It has been pointed out how Hopkins recognized the significance of his discovery and designated the unknown substance or substances which the milk furnished to the advantage of his animals, as "accessory" food substances. These experiments were conducted in 1906 but were not described until 1912. In the meantime Hoist had made his classic demonstration of the relation of scurvy to diet, and Funk and Suzuki had come forward with their extension of the studies of Eijkman and of Schaumann, and had coined the terms "vitamine" and "ory-zanin" respectively. In the minds of many nutrition investigators these were observations in the field of pathology rather than of normal nutrition.

The results of the feeding experiments with cattle described in Chapter II (A Biological Method For The Analysis Of A Foodstuff. 17. Mccollum'S Experiments Not Verified By Osborne And Mendel) are sufficient to illustrate the fact that studies with ordinary foods such as wheat, maize, etc., could never have been made to reveal the secrets which lay hidden in the field of nutrition. The results of those studies amply demonstrated that the persistent efforts of McCollum and Davis from 1907 to 1915 in seeking to discover the reason for the failure of young animals to grow on diets consisting of purified food substances was the most profitable line of attack for securing an insight into the number and natures of the factors which enter into the make-up of an adequate diet.