From time immemorial substitutes for human milk have been sought in the mammary secretions of other animals. The inadequacy of such substitutes has been made apparent by the distinctly higher incidence of disease and death among artificially fed babies. Early attempts were directed toward the correction of the grosser difficulties. By variously modifying and diluting the substituted milks—more particularly cow's milk—these have been rendered more acceptable to the digestion and quantitative needs of the infant. As a result, artificial feeding in the hands of the skilful worker has been fairly successful if measured in terms of disease and death. But so concerned have we been with the more obvious disturbances that little attention has been paid to the possible deficiencies of these diluted milks which may render them greatly inferior to human milk as far as their growth promoting factors are concerned, although experience has taught that the addition