~Diluents.~--Barley and oatmeal water are used as diluents to the amount of one-fourth or more of the mixture. Oatmeal water or jelly is used more during the winter months than in the hot summer months. As the fat content of the oatmeal gives it a more laxative effect, it is undesirable to use it at the season in which the summer diarrheas are prevalent. Barley water has something of a colloidal action upon the casein, causing the curds to be finer and less tough in character. Both barley and oatmeal water are used in place of plain water for babies when this colloidal effect upon the curd of the milk is desired, also where the weight of the infant shows a disposition to remain stationary, especially where there are no other symptoms to account for the lack of gain. Whey is used with babies who cannot digest the insoluble protein of cow's milk. This is often the case in premature babies and is manifested by a persistent vomiting of curd. The energy requirements are obtained by the addition of cream and lactose to the whey. ~Buttermilk Mixtures and "Eiweissmilch."~--It is often found desirable to use some other form of milk than whole, top, or even skimmed milk, and for this purpose lactic acid, milk and the albumen or "Eiweissmilch" are substituted. In the buttermilk mixtures the precipitation of the casein is brought about by lactic acid bacilli (Bulgarian culture). This prevents the coagulation of the casein into tough curds. Lactose buttermilk or lactic acid milk is used in the feeding of infants who have persistent green stools, and in cases of acute toxic diarrhea brought about through the action of gas bacillus. Buttermilk is more difficult to administer to babies than formulas made from plain milk by reason of its flavor. However, the results are remarkable in the above-mentioned conditions. ~"Eiweissmilch"~ is used in atrophic cases where there are bad green stools. ~"Homogenized Milk."~--Dr. Ladd of the Children's Hospital in Boston has presented many cases of infants who showed an intolerance for butter fat. These cases he has treated with formulas containing foreign fat, usually olive oil. This milk is subjected to a treatment which brings about a more complete emulsification of the fat than is possible in cow's milk, causing it to resemble in character the quality of the mother's milk. Homogenized milk has been used with success in cases where it was impossible to supply the infant with breast milk. The process is accomplished by the use of an apparatus known as an "homogenizer"[72]; in this machine the fat globule is crushed and so finely divided as to prevent its re-formation. The greatest drawback to the use of this process lies in the scarcity of available machines. Cod liver oil is now used in many cases where the infant shows a failure to gain or is in possible danger of developing rickets, with the homogenizer it is possible to add the oil to the formula, thus facilitating its use.