Milk a product of evolution designed specifically for the nutrition of infant mammals. It bridges the nutritional gap between intrauterine dependence and extrauterine independence. The same nutrients are present in the milk of all species, although in different proportions. Such quantitative differences appear to be an adaptation to the nutritive requirements of the young of each species. At the beginning of this century, Bunge1postulated that the chemical composition of the milk of each species was correlated with the composition of the newborn. Such a correlation, if any, not apparent. At about the same time, Abderhalden2suggested a parallel between milk composition and maturation rate of the infant mammal. However, Brody3noted that the relationship is complicated by many factors, evolutionary and physiologic. The situation too complex for a simple generalization. In spite of marked quantitative differences in the milk composition of different species,