It requires more acid to precipitate the proteid from woman's milk than from cow's milk. Giving a nursing woman an excess of nitrogenous food does not increase the albuminoid elements of her milk so much as the fats, while giving fatty or rich food in excess does not increase the cream or other ingredients of her milk - it may, indeed, diminish them by disordering her digestion. The nursing mother's diet must therefore be plain but substantial, especially in regard to animal foods. Excessive fat or proteid in the milk disorders the infant's digestion.

The following analyses illustrate the extent of possible variation in good specimens of human milk:

Eight Human Breast-Milk Analyses (C. Harrington) (Infants All Digesting Well And Gaining In Weight)

For the analysis of human milk about half an ounce is required, drawn from the middle nursing period, for the milk becomes progressively richer during nursing.

Prof. Albert H. Leeds (American Text-book of the Diseases of Children, pp. 42, 43) has shown, by a table of analyses of milk from eighty women of different nationalities, ages, and periods of lactation, that although "the average amount of nitrogenous matters [albuminoids] is somewhat greater at beginning of lactation, the difference is not very marked.... There is no progressive change in the composition of milk during lactation, but after the function has been normally established the milk remains substantially the same during the entire period.... The child obtains more nutriment day by day, but it is by spontaneously increasing the quantity according to the best rule, which is that of normal appetite, and not by absorbing stronger and stronger food".

Somewhat different conclusions are reported by Vanderpoel Adriance and John S. Adriance; based upon analyses of the milk of 120 healthy mothers at the Nursery and Quids' Hospital, New York. In each case the sample was obtained after allowing the infant to nurse for two minutes, and periods studied were from the second day to the fifteenth month of lactation. They found that of all the ingredients of human milk the fat varies most, and varies throughout lactation, the extremes being 7.61 and 1.31 per cent. The fat bears a rough general proportion to the proteid of 3: 1. The carbohydrate, which weighs during the middle period of lactation more than all the other solids together, increases throughout lactation, and ranges from 5.35 to 7.95 per cent.

The proteid percentage is highest during the colostrum period, when it may reach 8.60 per cent, and falls rapidly towards the end of lactation. Pfeiffer found it as low as 1.52 at the seventh month, buttfcis is extreme reduction. It is increased by worry and nervousness and by lack of exercise; it is lessened by reduction of meat in the dietary, and vice versa. The salts diminish from.27 per cent on the second day to.14 at the fifteenth month.

The average specific gravity is given by Adriance as 1.030. It is lessened by increase of fat and increased by increase of proteid.

Human colostrum differs from the later milk as follows: It contains colostrum corpuscles which remain from seven to ten days; it has a yellow colour, which disappears with the corpuscles; it is laxative to the infant; its fat varies greatly; the quantity of sugar is lowest and of proteid and ash highest of any period of lactation.

Drugs In Human Milk

Many drugs are excreted through the mother's milk, and it is often the case that an infant is affected by suckling such milk. It is possible to act upon infants through this medium, but the strength of solution in which the drug reaches them is far too uncertain. An infant has been killed by nursing from a mother who had taken an overdose of laudanum (Fletcher). Acids given to a nursing mother may cause colic in the child. Neutral salts loosen the bowels, and potassium salts act as diuretics for infants when taken by the mother. Aromatic oils, and probably all volatile oils, reappear in the mother's milk. The agreeable taste of some of these substances causes the child to suck harder, and excites thereby a reflex stimulation of the mammary glands to further secretion.

Among other drugs which have been determined in the mother's milk after ingestion by the stomach are: Senna, rhubarb, scammony, sulphur, castor oil, ammonium salts, turpentine, copaiba, anise, dill, garlic, wormwood, and jalap. Antimony passes readily into mother's milk, and should be given with caution to nursing women. Potassium iodide, corrosive sublimate, and other mercurial salts, arsenic, zinc, and lead, all may be excreted in the milk at periods varying from four hours to several days after their administration and continue to be eliminated for a day or two after the drug has been withheld.

Vegetable acids give rise to carbon dioxide in milk. If nursing mothers partake freely of fresh fruit and green vegetables their milk may gripe and purge their infants. Violent exercise and violent mental emotion are harmful to the milk.

Goafs milk is the least digestible and nutritious of milks, although it contains the most solids. It is scarcely used at all in the United States except sometimes by very poor foreigners, as it is in Switzerland and other mountainous European countries, and for some Eastern tribes it is a staple variety of milk. Cheese is also made from it on a large scale. It has a peculiar strong odour and taste, which are disagreeable to those who are unaccustomed to it, and which are partially expelled by boiling. They are due to a substance called hircin or hircic acid.

Goat's milk contains an excess of fat, and for this reason is too 6 rich for infant food, and gives rise to vomiting and diarrhoea. The coagulae formed by it are very tough.

Ass's milk contains the least solids of all the edible milks, except mare's milk, and is poor in casein and fat. It has a fair proportion of sugar, more than cow's milk but less than human milk. Ass's milk is sweet and easy of digestion, although it has a tendency to cause diarrhoea.

Experiments in the feeding of children direct from asses were conducted in Paris in 1883 at the Hospice des Enfans Assistes. One ass sufficed to nourish three infants besides her own foal. The asses were kept near the ward and the infants were brought to them to nurse. Syphilitic infants belonging to a class in which death had been the invariable rule were thus nursed, and 70 per cent were saved. The experiment does not seem to have found favour elsewhere. Goats were first tried, but proved of no service for direct nursing.

Mare's milk, like ass's, contains less proteid and less fat, but more lactose than cow's milk.

The casein of mare's milk is intermediate in digestibility between human and cow's milk. Both ass's and mare's milk are used in the steppes of Russia and in Siberia for the manufacture of koumiss. (See Koumiss).

Reindeer milk contains 18 per cent of solids, and, generally speaking, those domestic animals living farthest north have the most solids in their milk.