The sterility produced by simplified diets low in vitamin E is often delayed in its appearance because of the fact that traces of vitamin E exist in most of these dietaries, combined with the fact that young animals also begin life with proved traces of vitamin E derived from the mother. We have called this phenomenon "initial fertility." If the diet contains a fat known to possess vitamin E (e. g., butter), initial fertility may exist in most members of a group and be prolonged; with fats low or lacking in vitamin E (e. g., lard) initial fertility also often occurs but never to the same extent. On the diet that we have called our basic ration (B. R.), consisting of casein, 18; corn-starch, 54; lard, 15; butter, 9; salts, 4, and yeast, from 0.5 to 0.7 Gm. daily, initial fertility may be so high as to enable 40 per