The great difficulty in connexion with the question of diet in adult life is that we have no authoritative standard which will command general acceptance. For infants, on the other hand, we have both a standard diet and a food supplied by nature in the shape of breast milk. Experience has shown that this natural food for infants is also the best food, and further that when artificial feeding is called for, the more closely the food approximates to breast milk, the better will be the result. Breast milk is becoming more and more of a luxury for infants, at least amongst certain sections of the population, and the unanimous voice of the medical profession on the importance of breast-feeding is but too little heeded. Nevertheless the young practitioner, however diffident he may be on other subjects, is fully justified in dogmatically asserting the immense importance and necessity of breast-feeding for the welfare of the infant. It is a matter on which the medical profession has made up its mind once for all. Certain cases arise in which breast-feeding cannot be carried out and some artificial food must be used. Here again experience has shown that fresh cows' milk, suitably modified so as to resemble breast milk as closely as possible, is the best substitute at present known. Its use, however, is accompanied by many difficulties and dangers unknown in connexion with breast-feeding. In other cases, where the supply of breast milk is deficient, it is beneficial to supplement this source of supply with a certain number of meals composed of cows' milk. This is known as mixed feeding. These three methods, breast-feeding, mixed feeding, and feeding with cows' milk are the ones in common use in this country and we shall now consider them more in detail.