Casein . . . . . . . . . . . . . . . 18 18 18 18
Lactose . . . . . . . . . . . . . . . 20 0 0 0
Dextrin . . . . . . . . . . . . . . . 0 59 74 74
Starch . . . . . . . . . . . . . . . 31 0 0 0
Agar-agar . . . . . . . . . . . . . . 5 2 2 2
Egg (see above) . . . . . . . . . . . 0 0 * 0
*1 gram extract every other day

II and III (from _Journ. Biol. Chem._, 1915, xxiii, 231). These
charts show the effect (II) of the addition of as little as 2 per cent
wheat embryo as sufficient to secure normal growth when it serves as a
supply of the B vitamine. Chart III shows that even when the wheat embryo
is increased to 30 per cent it is inadequate for growth unless the A is
also present. The diets were as follows:

Dextrin . . . . . . . . 69.3 52.8
Salt mixture . . . . . . 3.7 2.6
Butter fat . . . . . . . 5.0 0.0
Agar-agar . . . . . . . 2.0 2.0
Casein . . . . . . . . . 18.0 12.6
Wheat embryo . . . . . . 2.0 30.0]

These results linked up with those of Stepp and Mendel and showed that
butter fat and egg yolk fat contained a growth factor which was missing in
other fats. McCollum named this the "unidentified dietary factor fat-
soluble A."

In the same year F. G. Hopkins in England announced that the addition of 4
per cent of milk to diets consisting of purified nutrients would convert
them into growth producers. This was too small an amount to admit of