In a recent communication I1reported that, while a cold 75 per cent alcoholic extract of 6.5 Gm. of whole wheat embryo per animal daily furnishes enough vitamin B for excellent growth, it is necessary to supply the same alcoholic extract of at least 22.4 Gm. of wheat germ per lactating rat daily to furnish enough vitamin B for normal lactation. I have now developed a quantitative biologic method, employing synthetic diets composed of purified food substances, for the study of vitamin B in lactation. The details of the method will be published soon elsewhere, but essentially the technic is as follows: Mothers with their litters born from our stock colony receiving stock ration 11are separated on the day of the birth of the young, the litter reduced to six and then placed on the following vitamin B deficient diet: casein (purified), 20.0; agar-agar, 2.0; butter fat,