The only food that meets all of the infant's requirements is human milk. This is especially true during the first few weeks of life, when any artificial feeding is often a dangerous substitute. Breast feeding should be encouraged in every way, even if only for a short time. The pessimism about increasing inability of mothers to nurse their babies is not entirely well founded. From the consultations de nourrissons in Paris, and from many other sources, comes increasing evidence that many more mothers would be able to nurse for many months, and nearly all of them for many weeks, if they were properly encouraged, and properly taught how to nurse, and how to care for themselves and for their babies.

1. Human Milk

Human milk is a bluish white, alkaline or amphoteric, germ-free fluid, with a specific gravity of 1,026 to 1,036, with an average of 1,031 at 60° F. (Holt).

A. Colostrum

During the first two or three days the infant receives daily only a few ounces of a secretion from the breast, called colostrum. It is heavier, with a specific gravity of 1,030 to 1,040, thicker and more yellow than later milk. It contains three or four times as much proteid, about one half as much sugar, and a little more salts. When boiled it forms a thick coagulum. It contains characteristic large, irregular, granular masses, the colostrum corpuscles, that are four to five times as large as the larger fat globules. They are probably fat-laden leucocytes that are endeavoring to relieve milk stasis, and disappear normally during the first two weeks when the flow of milk is well established and the breast emptied at intervals.

B. Composition

After the first few weeks human milk varies but little in composition throughout the whole period of lactation if the breasts are emptied regularly. It contains about an average of fat four per cent; sugar seven per cent; protein 1.5 per cent; salt 0.2 per cent; water 87.3 per cent (Holt). The fat varies most and is considered the measure of richness of the milk. It varies from two to six and even ten per cent in different individuals, and in the same individual at each nursing, the first part containing little and the last part very much fat. It is composed of the neutral fats, olein, palmitin, and stearin, with a small amount of fatty acids. It occurs as minute, round, refractive globules of fat, varying considerably in size and suspended in the form of an emulsion. Closely connected with the fat and possibly also with a protein is a phosphorus-containing body called lecithin, that is much more abundant than in cow's milk, and is probably of importance in metabolism.

The proteins consist of casein, lactalbumin, lactoglobulin, and probably others, such as lecithalbumin and lactomucin. The casein is a phosphorus-containing protein combined with lime and forms a little less than one half of the total protein. It is imperfectly coagulated by rennin, by acids, and by certain mineral salts, forming a fine flocculent precipitate. The lactalbumin coagulates on heating, but is uninfluenced by rennin. The lactoglobulin is found only in small amounts, except in colostrum. The proteins vary but little during lactation, falling slightly in quantity toward the end.

The sugar is milk sugar or lactose. It is the most constant food element throughout lactation as well as in different individuals, probably because of its important role as a heat producer in the body.

The salts are combinations of K, Na, Ca, Mg, NH4, Fe, O, N, P2O5, CI, CO2, with traces of Fl, I, Mn, and others. They gradually lessen in amount.

Citric acid is always present in small amounts.

C. Immunizing Bodies

Human milk contains all the antitoxins, alexins, etc., found in the mother's blood serum often in definite proportions. These are known clinically to have a decided influence in protecting the nursing infant against infections. The baby that nurses is in this respect a part of its mother.

D. Ferments

Milk contains many ferments, such as amylo-lytic, possibly glycolytic, proteolytic, and coagulating ferments; lipase that has a fat-splitting action, reductases, and others. How much importance these enzymes have in nutrition is not known.

2. Quantity Of Breast Milk Required

The quantity of breast milk required by healthy, thriving infants has been determined by numerous observers who have weighed such babies before and after nursing, for many months in some cases. The daily amounts taken have been found to vary quite definitely with the weight of the baby, and with its age. During the first month this daily amount can be placed at one fifth to one sixth of the baby's weight, gradually lessening to one eighth after the sixth month. From such observations in healthy infants Heubner determined the number of calories per kilogram (2.2 pounds) of body weight taken daily during various parts of the first year. This so-called energy quotient - i. e., the number of calories per kilogram of baby taken daily - he places at 100 during the first six months, gradually lessening toward the end of the year to about 80 or 85, with 70 as approximately the energy quotient on which the child will neither gain nor lose. The caloric value of one ounce of human milk can be placed at 21.

3. Hygiene Of Maternal Nursing

During the first two or three days the newborn child gets only a scant supply of food, from one to three ounces daily of colostrum. No other food should be given during this time except water. It will be remembered that the "physiological fecal flora" occurs only when breast milk is taken, and any other food would establish a flora that might be extremely dangerous to the delicate organism. It is for this reason, too, that every infant should get breast milk for a time, if only for a few weeks or even days. If the child is vigorous and has no fever (inanition temperature) on the second or third day, it is best to await serenely the free flow of milk that commonly occurs on the third or fourth day, rarely later. If there is fever, or the milk is delayed beyond this time, or the infant seems weakly, it is necessary to give temporarily some food, preferably milk from another mother, or a weak cow's milk mixture, or a five-percent milk-sugar solution.