It should be remembered that in Stepp's investigations the element of growth was not included. He studied the nutritive requirements for maintenance of mice and pigeons, whose growth was complete. His results are, nevertheless, of great interest because they agree with those McCollum and Davis obtained with growing rats (5). They established the fact that for the mouse and rat, two substances at least, other than the conventional components of the diet, protein, fat, carbohydrate and salts, are essential for satisfactory nutrition. Stepp, in his early studies, interpreted the results to indicate that only certain lipins were necessary to supplement successfully a diet of purified food substances of the hitherto recognized group. When Funk demonstrated the necessity of a protective "vitamin" for the prevention of beri-beri, Stepp extended his studies to include "vitamins" in addition to lipins. Finally, in November, 1915, he presented data showing the necessity of "vitamins" as well as certain other substances soluble in alcohol (6). These are present in many natural foods. McCollum and Davis simultaneously published a paper in which they demonstrated the necessity for growth in rats, of a fat-soluble and a water-soluble substance. It may be well at this point to call attention to the bearing of the studies of Stepp on the question whether there are any demonstrated differences in the nutritive requirements of mammals during growth as contrasted with those for maintenance in the adult.