In the absence of breast milk, the substitute which has gained universal acceptance and approval is pure, fresh, cows' milk. It is not however to be regarded as a perfect substitute, and while one may usually look forward to a placid career, free from digestive troubles, for a breast-fed infant, the child who is started early on cows' milk will probably encounter many troubles in connexion with the digestive organs. Cows' milk is meant primarily for the calf, and amongst other features its composition is such as to suit the rapid growth and activity of that animal. This explains the richness of cows' milk in proteins and mineral matters (Hutchison). A calf doubles its weight in the first forty-seven days of life while an infant takes four times as long. The following table shows the differences between average breast milk and average cows' milk.
Woman's Milk (fresh).
Cows' Milk (fresh).
Amphoteric (more alkaline than acid).
Amphoteric (more acid than alkaline).
87 to 88 per cent.
86 to 87 per cent.
Mineral matter .
0.20 per cent.
0.70 per cent.
Total solids .
13 to 12 per cent.
14 to 13 per cent.
4.00 per cent. (relatively poor in volatile glycerides).
4.00 per cent (relatively rich in volatile glycerides).
Milk sugar .
7.00 per cent.
4.75 per cent.
1.50 per cent.
3.50 per cent.
(1) Caseinogen .
1/3 to 1/2 of total proteins.
2.66 per cent.
2/3 to 1/2 „
0.84 per cent.
Coagulation of proteins by acids and salts
With great difficulty.
Curds small and flocculent.
With less difficulty. Curds large and tenacious.
Coagulation of proteins by rennet
Do not coagulate readily.
Action of gastric juice
Proteins precipitated but easily dissolved in excess of the gastric juice.
Proteins precipitated but dissolved less readily.
- From Rotch's Pediatrics.
The differences between the two milks call for careful examination for certain modifications of cows' milk, based on these differences, have to be employed. The great problems of infant feeding centre around the question as to how these modifications may be most satisfactorily carried out. We shall first consider the differences in the two milks, and then pass on to the modifications in common use. The specific gravity and the amount of water are practically the same in the two fluids.
The proteins in breast milk amount to about 1.50 per cent, while those in cows' average 3.50 per cent. The excessive amount of protein in the latter is an important difference, and calls for reduction in artificial feeding. Both milks contain caseinogen and lactalbumin, but while in cows' milk the caseinogen markedly predominates, in breast milk the proportions of the two are nearly equal. As lactalbumin is a much more digestible protein than caseinogen the difference is an important one. Further the caseinogen of the two milks reacts differently to acids, the curd formed by breast milk being soft and flocculent, and soluble in excess of acid, while that of cows' milk consists of large masses which do not easily dissolve in excess of acid.
The chief difference between the two milks as regards the cream is that fat globules of breast milk are smaller and form a finer emulsion than those of cows' milk. Hutchison states that the fat in breast milk has a lower melting point and is therefore more easily digested. The amount of fat in average breast milk is 4 per cent and in cows' milk 3.75 per cent.
In both milks sugar is the carbohydrate but there is from 2 to 3 per cent more in breast than in cows' milk. The amount of sugar in the latter must be increased to bring it up to nature's standard. In both cases lactose is the sugar present.
Breast Milk Is Sterile , and as it passes direct to the infant there is no opportunity for contamination with microorganisms. Cows' milk, on the other hand, as commonly employed is invariably infected with many organisms which develop in it with great rapidity. These organisms may be pathogenic or nonpathogenic, the latter however considerably altering the quality of the milk. The pathogenic organisms are the tubercle bacilli, derived from tuberculous cows or deposited in the milk during transit, and those of typhoid fever, scarlet fever or diphtheria, from infected water, utensils, or hands with which the milk has been brought in contact. These are accidental contaminations and are by no means necessarily present in cows' milk. The observation of proper precautions as regards the health of the cows and of those dealing with the milk, and of cleanliness in the whole management of the milk supply, will serve to prevent such contamination. Unfortunately the necessary precautions and cleanliness are but seldom observed, and many modifications of milk have been adopted to meet this danger. The non-pathogenic bacteria are chiefly of the lactic acid forming group which cause the souring of milk by their action on the milk sugar. These and other organisms reach the milk during the time the milk is exposed to the air or from infected vessels in which it is placed, and increase with great rapidity. Under present conditions it seems impossible to exclude them altogether, and our efforts must be directed to keeping down their numbers as much as possible. Holt states that in one of the finest dairies in America, a Walker-Gordon farm, it was found possible to limit the number of bacteria present in the milk to an average of 5,000 per cubic centimetre at the end of sixteen hours. The bottled milk from high-class dairies was found to contain from 10,000 to 100,000, while from mixed dairies the milk in cans was found to contain from 100,000 to 400,000 bacteria per cubic centimetre, the latter estimate being often reached in very hot summer weather. It is plain that no modification will render such milk a proper food for infants. The question is rather one for the public health authorities, who should regulate the sale of milk in such a way that milk containing more than a certain number of bacteria would be declared unfit for human use.
A Certain Amount Of Coarse Contamination is present in cows' milk which does not occur in breast milk. This takes the form of hairs and surface filth from the cows, of dirt from the hands of the dairy workers, and of dust which is deposited during the exposure of the milk. A certain amount of this can be and ought to be removed by filtering through fine cloth, as it is by no means a desirable addition to the milk. In the best dairies the amount of contamination is much reduced by the observation of strict cleanliness in the whole process of milking and the immediate storing of the milk in airtight vessels.
Human Milk Is Alkaline , while the reaction of cows' milk is acid, and the acidity increases with the formation of lactic acid. It is probable that the slight degree of acidity present in cows' milk is not of great importance, as gastric digestion is carried on in an acid medium, and the salivary secretion is slight. If the milk is soured by the excessive development of lactic acid, it is not fit for use. The practice of adding an alkali simply to render cows' milk alkaline has rather fallen into disuse in the feeding of healthy infants. The addition of lime-water as a routine proceeding is not to be recommended as cows' milk contains normally a large amount of lime salts.
There is from three to four times as much mineral matter in cows' as in breast milk. The chief salts are those of calcium and phosphorus. Hutchison states that in human milk nearly all the phosphorus is in organic combination, while in cows' milk less than half is. Calcium salts are much more abundant in cows' milk than in breast milk, and this difference has an important bearing on the question of protein digestion, as will be seen later.