The age and the weight are of some importance, but the best guide is the condition of the child's digestive organs. One should always begin with a weak formula, particularly, (1) with an infant previously breast fed; (2) with one just weaned, as a child who has never had cow's milk must at first have weaker proportions than the age and the weight would seem to indicate; (3) with infants whose power of digestion is unknown. If the first formula tried is weaker than the child can digest, the food can be strengthened every three or four days until it is found what the child is able to take. On the contrary, if the food is made too strong at first, an attack of indigestion will probably follow. _How should the food be increased in strength?_ The first essential is that it be done very gradually; abruptly increasing the food usually causes a disturbance of digestion. It is never wise to advance more rapidly in strengthening the food than from one formula to the next one in any of the series given; with many infants it is better to make the steps of increase only half as great as those indicated (page 72). _How rapidly should the food be increased in quantity?_ The increase should not be more than a quarter of an ounce in each feeding; or from one and a half to two ounces in a day. _When should the food be increased?_ In the early weeks an increase may be necessary every few days; in the later months sometimes the same formula may be continued for two or three months. It is, however, impossible to give a definite rule as to time. One cannot say with any child that an increase is to be made every week or every two weeks. A much better guide are the conditions present. The signs indicating that the food should be increased are, that the infant is not satisfied, not gaining in weight, but is digesting well, i.e., not vomiting, and having good stools. One should not increase the food, however, so long as the child seems perfectly satisfied and is gaining from four to six ounces a week, even though both the quantity and the strength of the food are considerably below the average; nor should the food be increased if the child is gaining from eight to ten ounces a week, even if he seems somewhat hungry. The appetite is not always a safe guide to follow. _How can one know whether the strength or the quantity of the food should be increased?_ In the early weeks it is well first to increase the strength of the food, the next time to increase the quantity, then the strength again, etc. After the fourth or fifth month, the quantity, chiefly, should be increased. _If a slight disturbance or discomfort occurs after the food has been strengthened, is it best to go back to the weaker formula or to persist with the new one?_