In 1909 McCollum (26) introduced a new feature into experiments of this type by seeking to increase the variety of foodstuffs in the diet as far as possible, with the hope of obtaining success where others had failed to secure satisfactory nutrition in animals. In the series of experiments referred to the one condition which was required of every organic component of the ration was that it should be free from phosphorus in any form. This condition was practically met. The only source of phosphorus in the diet was finely ground tricalcium phosphate, a natural mineral.

14. A Mistaken Conclusion Which Stimulated Research In A New Direction

This paper is deserving of special notice because it reported the first successful growth experiments with a food supply which was at that time considered as essentially a mixture of purified foodstuffs, every one of which could be named. It seemed to demonstrate that the view, which had long held sway, that the only substances necessary in the diet are proteins, carbohydrates, fats and certain mineral salts, was indeed well founded. It appeared to prove that the cause of the failure of the earlier experiments of this type was due to the lack of palatability of the food, which led to failure of the animals to ingest sufficient quantities of food. This was one of the conclusions of the author, but it has since become apparent that this viewpoint was a mistaken one.

The proteins employed were edestin from the hemp seed and zein from maize. Corn starch, wheat starch, milk sugar, glucose, cane sugar, butter fat, bacon fat, and cholesterol, a substance found in most body tissues and having physical properties similar to fats, together with the ash constituents, made up the food supply. No effort was made to feed a constant mixture. On the contrary, the diet was changed from day to day as far as possible in order to prevent the dreaded loss of appetite. On this food supply several young rats gained in weight, one somewhat more than doubling its weight in fifty-six days. These results were interpreted as meaning that growth had actually been induced by a mixture of purified food substances, where all previous attempts had failed. The only difference between the experimental diet used in this study and those of the earlier investigators appeared to be in the palatability factor. Important deductions were drawn from these results concerning certain synthetic reactions which the body tissues could accomplish. Five years later it became apparent that the cause of the growth of this group of animals lay in the chance inclusion in the diet of milk sugar, which was not as pure as it was supposed to be, and to the inclusion of butter fat. Each of these we now know furnished a substance indispensable for either growth or maintenance. But a surprisingly small amount of each of these is necessary in order to induce the maintenance and the growth secured in these experiments.