As regards the digestibility of all its ingredi ents, milk is one of the most digestible of animal foods. it has been found that on an average an adult digests about 97 per cent. of the pro tein. 95 per cent. of the fat. and 98 per cent. of the carbohydrates of milk. .‘ccortling to American experiments. a child one year old eating milk digests on an average only about 90 per cent. of the protein. 96 per cent. of the fat, and 813 per cent. of the carbohydrates of cows' milk. When milk is taken into the stomach it is speedily curdled by the action of the pepsin and acid of the gastric juice. When eaten alone or in large quantities, the casein gathers in large hunps, which in some persons may be difficult to digest. This is partieularly the ease with in fant.: and with adults whose digestion is weak. The casein of human milk is precipitated in more floectilent form than that of cows* milk, and is thus more easily digested and does not cause irritation. Lime, which tends to prevent the eurdling of the casein of cows' milk in lumps. is frequently added as lime water to milk that is to be fed to infants or to adults of delicate diges tion. The results of experiments upon the effect of cooking milk are conflicting. The more corn 111Im experience seems to indicate that cooking r heating the milk renders it more difficult to digest. Some persons. however, eannot take fresh milk with comfort, hut ean digest boiled milk.
Milk is often said to be a `perfect food.' It is so for the young of the species of animal producing it, but there are three reasons why it eannot be considered a perfect food for adults. I 11 The proportion of water is so large that great quatititil.s 1 to 5 would have to be consumed each day in order to obtain the necessary nutrients. (2) The protein is present in rather large quantities as compared with the fats and carbohydrates. Thus the milk necessary to furnish the 0.28 pound of protein per day, estimated to be required by a loan at moderately active work, would yield only 2700 calories of energy, while milk in sufficient quantity to fur nish the 3400 calories estimated as necessary would yield 0.34 pound of protein. (3) It is a well recognized fact that the digestive functions require that food itself, besides the water taken with it, shall have a certain bulk. Cattle cannot generally be maintained in health upon a con densed ration such as grain; they seem to require a certain distention of the stomach, such as is brought about by the fibre (cellulose or woody matter) of grass or hay. In like manner it seems desirable that man should have a certain amount of bulky material to produce distention or to pro mote peristaltic action of the intestines, or for other purposes not well understood. Of course. the nutritive constituents of milk, considered separately. are highly concentrated foods. While, therefore, milk alone cannot be considered as a perfect diet for adults, it is of special value as a food for invalids, because it is. a- a rule, easily taken, easily digested. and does not generally ir ritate the alimentary canal. Furthermore, a milk diet is more readily under the control of the physician both as regards quantity and quality than a mixed diet is. If for any reason a child cannot be nourished on mother's milk. the most useful substitute is modified milk. Various infant foods and milk substitutes have been proposed and are sold under divers trade names.
As a food for adults cows' milk is unusually well adapted for use in connection with other foods, either in its uncooked form in tea and coffee, as a beverage, as bread and milk, etc.. or incorporated and cooked with other materials.
In many culinary products it can be used instead of water. Analysis of bread, rolls, etc.. made with milk would show about one-tenth more pro tein and one-twentieth more fuel value than bread made with water. Milk is very generally used in many kinds of cake and pastry and in custards. Where desirable from economical rea sons, or as a means of increasing the proportional amount of protein in a diet, skint milk can be advantageously substituted for whole milk. At the price ordinarily paid in our large eitics milk is a food of reasonable cheapness, and at the prices prevailing in small cities and country towns it is an economical food. Condensed milk is a more nutritious food, pound for pound, than fresh milk. since it has been concentrated by evaporation. It is. however. usually diluted be fore it is used, and then approximates fresh milk or less closely in composition and food value. If the condensed milk contains added sugar its carbohydrate content is, of course, high er than that of unsweetened condensed milk, and when diluted. proportionally higher than that of fresh milk. Cream, which contains the greater part of the fat of the milk, as well as some pro tein and carbohydrates, is chiefly valuable in the diet as a source of energy. Curds obtained in the manufacture of cheese are eaten to a limited extent. They consist quite largely of the casein of milk, and hence supply the body with building material as well as energy. Butter and cheese (qq.v.), the principal milk products used as food. are of great importance as articles of diet.
The former, consisting almost entirely of fat, supplies energy; the latter, containing protein in addition to fat, supplies both building material and energy.
There are at least four distinct fermented bev erages prepared from milk—kephir 1:011 miss matzoon (q.v.), and leben. They are properly classed as food beverages, and are often recommended for the sick and for convalescents.
number of special foods are made from the dry casein of milk and are used to a considerable extent by physicians to supply protein in it readily digestible form. The albuminoids of milk arc used in the manufacture of egg substitutes. ,Milk sugar prepared from whey is an important article of diet for invalids and is used in medi cine and in other ways.
BIBLIOGRAPHY. The literature of milk is exBibliography. The literature of milk is ex- tensive. In addition to the publications of the Dairy Division of the United States Department of Agriculture and the bulletins of the various ex periment stations, the following works may be mentioned: Fleisehmann, The Book of the Dairy, A Manual of the Science and Practice of Dairy Work, trans. by Aikman and Wright (London, 1890) ; Wing, Milk and Its Products (New York, 1897) ; Snyder, Chemistry of Dairying (Easton, Pa., 1897) ; Aikman, Milk: Its Nature and Com position: A Handbook on the Chemistry and Bacteriology of Milk, Butter, and Cheese( London. 1895) ; Richmond, Dairy Chemistry: :I Practical Handbook for Dairy Chemists and Others Haring Control of Dairies (London, 1899) ; Russell, Dairy Bacteriology (Madison, Wis., 1897) ; Conn, Bacteria in Milk and Its Products (Philadel phia, 1903) ; Farrington and Woll, Testing Milk and Its Products (_Madison, Wis., 18981; Non rid. Pasteurization and Milk Preserration ( Win netka, Ill., 1901) ; De Rothschild, Bibliographia Lartaria (contains 8375 titles) (Paris, 1901) ; Hogan. How to Feed Children (Philadelphia. 1896) : Holt, Diseases of Infancy and Childhood (New York. 1899) ; Chapin, Theory and Practice of Infant Feeding (New York. 19021; Farmer's Bulletins Yos. 42, 74. United States Department of Agriculture.