When it becomes necessary to substitute some other food for the breast milk, it means that the milk of some other mammal must be modified for the purpose. The most convenient and abundant source of supply is the cow.

While in many respects cow’s milk is similar to mother’s milk, it is in reality quite a different product. Mother’s milk is taken, undiluted, directly from the breast, while cow’s milk is given from a bottle, hours after milking, and not only must it be diluted, but certain ingredients must be added to aid its digestibility.

When taken into the stomach in its natural state, mother’s milk is a liquid, while under the same conditions, cow’s milk forms a semisolid gelatinous mass.

It is essential that the milk should be as fresh, clean, and free from bacteria as possible, and this can be approximated only in certified milk. This milk is required by law to have its constituents definitely standardized. Thus, there must be 4 per cent of fat, 4 per cent of protein, and 4 per cent of sugar, and it must be so free from bacteria that not more than 10,000 per cubic centimeter can be found. The cattle also are tuberculin tested. The following comparison is from Holt:

Mother’s MilkCow’s Milk
Sp. Gr.av. 1.031av. 1.031.
Fat4.  %Fat4.  %
Protein1.50%Protein3.50%
Sugars7.  %Sugars4.50%
Salts.2 %Salts.75%
Water87.3 %Water87.3 %
ReactionAlkalineReactionAcid
BacteriaVery fewBacteriaMany
Both range from 1.026 to 1.06.

Fig. 130.—Elements of human milk. (Eden.)

The fats are substantially the same, but the fat of cow’s milk is less easily digested than the fat of mother’s milk.

The protein of mother’s milk is virtually half lactalbumin and half casein, which is only slightly coagulated into soft flocculent curds by the action of rennin and acids, while the casein of cow’s milk is nearly three times greater in amount than the lactalbumin and is coagulated into coarse, tough curds.

The sugars in both cases are lactose in solution, but mother’s milk contains a much higher percentage.