The significance of the observation that guinea pigs develop scurvy when fed on oats and milk seemed even more important to McCollum and Pitz (13) than to Jackson and Moore. McCollum and Davis (14) had in 1915, as the result of extensive studies on the nutrition of the rat, formulated the working hypothesis that the simplest diet which can support normal nutrition in this species is one which fulfills the following conditions. It must contain sufficient protein of the "complete" type; adequate amounts of nine mineral elements in appropriate combinations (Na, K, Ca, Mg, Cl, P, S, Fe, I); a source of the carbohydrate glucose, and two dietary factors of undetermined chemical nature, which McCollum and Kennedy (15) provisionally called fat-soluble A and water-soluble B. These were recognized as belonging to the class of food substances which Funk (16) had designated by the term "vitamine," and for the existance of which he had positive evidence only in the case of the anti-beri-beri substance (water-soluble B) with which polyneuritis in birds and beri-beri in man had been successfully treated. The history of the investigations which led to the discovery of these has been presented in Chapter II (A Biological Method For The Analysis Of A Foodstuff. 17. Mccollum'S Experiments Not Verified By Osborne And Mendel).

McCollum had found that a diet of oats and milk sufficed to maintain a rat in a state of health for a long period, without any evidence of disease. When McCollum and Pitz, independently of Jackson and Moore, observed that guinea pigs confined to a diet of oats and milk quickly succumb to scurvy, they found it difficult to believe that the disease could be due to the lack of a specific substance, for milk alone suffices as the sole food for all young mammals during a critical period of their lives. It was difficult to accept the view that anything essential for normal nutrition was absent from milk and oat mixtures.

They further observed that their guinea pigs which were suffering from scurvy developed impaction of the cecum when the condition was brought about by feeding milk and oats, both of which are constipating foods. They, therefore, offered the tentative explanation that injury to the cecum of this species is of primary importance as a factor in the etiology of scurvy. They were inclined to accept the view of Jackson and Moore that the cause of the disease was an invasion of the tissues by bacteria, made possible by the damage to the cecum as a result of the retention of feces. The observation that paraffin oil or cathartics sometimes saved scorbutic animals from death lent support to this view.