One of the major problems in the use of cow's milk for infant feeding has been the physical character of the curd. This phase of the subject has been stressed repeatedly by Brennemann,1 and the various methods for modifying the curd have been utilized clinically with good results. The three main factors concerned with the type of curd formed from cow's milk in the infant's stomach are casein, rennin and calcium ions. When cow's milk is modified for infant feeding, one or all of the three factors are utilized in the methods of dilution with water or a solution of a protective colloid such as cereal water, addition of rennin, treatment with heat and acidification. Other methods, such as precipitating calcium ions by the addition of alkali (solution of calcium hydroxide and sodium bicarbonate) or forming a complex calcium salt by adding sodium citrate, are seldom used today.