3. It must be clean and free from disease germs; other organisms should not be present in excessive numbers. 4. It must be fresh; less than 24 hours old when it is delivered. All of this means that the milk must come from a herd of healthy, tuberculin-tested cows. The milk from a single cow may vary markedly from day to day but that from several cows is nearly constant. The stables and the cows must be kept clean, the udders carefully washed before each milking; the milkers themselves must wear freshly washed clothing, scrub their hands thoroughly and milk into sterile receptacles; the milk must be immediately covered and cooled to a temperature of 45° F. or 50° F. and kept there. Milk produced under such conditions is usually described as “certified milk” and is often prescribed as infant food without being pasteurized or sterilized. But if there is any doubt about the source of the milk and the method of its handling, it should be strained into a clean receptacle through filter paper or a thick layer of absorbent cotton and subsequently boiled or pasteurized. Whether certified or not, the milk should invariably be placed in the refrigerator, or some other place which has a temperature of 50° F., as soon as it is received, and _it must be kept cool and clean_. Keeping milk cool means keeping it at a temperature of 50° F. Keeping it clean implies cleanliness not alone of the milk itself but of your hands and the utensils that you use as well as the destruction of disease germs by pasteurization or sterilization. Among the germs which are likely to be present in infected milk are those that cause diarrhea, sore throats, typhoid fever, diphtheria and scarlet fever. When the doctor makes out the formula for the baby’s milk, he will adjust the proportions of the different ingredients to the baby’s immediate needs and digestive powers. But his careful estimations will be set at naught unless you are absolutely _accurate_ in preparing and giving the milk. Your invariable responsibility in connection with the baby’s milk, therefore, is to keep it _cool_ and _clean_ and be _accurate_. You will appreciate the necessity for modifying cows’ milk before giving it to your baby if you will note the differences between mother’s milk and cows’ milk as indicated by the following table and consider, too, why Nature has made these differences: _Mother’s Milk_ _Cows’ Milk_ Fats 3.5 to 4. per cent 3.5 to 4. per cent Sugar 6.5 to 7.5 per cent 4.5 to 4.75 per cent Proteins 1. to 1.5 per cent 3.5 to 4. per cent Salts .2 per cent .7 to .75 per cent Water 87. to 88. per cent 87. per cent