Milk-sugar, or lactose, has the same composition as cane-sugar, but differs from the latter in some of its chemical proper ties and is less sweet and less readily soluble in water. The amount of sugar is rather more constant than that of proteins, being usually between 4.5 and 5.25 per cent in normal milks. While the latter figure is rarely exceeded, occa sional samples may show considerably less than 4.5 per cent. In any genuine milk containing an unusually low percentage of solids-not-fat, the deficiency is apt to be principally in the milk-sugar. Such milk is apt to be yielded in case of fever or unusual excitement or fatigue, and may sometimes be obtained from appar ently healthy cows under normal conditions, especially during hot, dry weather.
Salts or Ash of Milk.— When milk is dried and burned there remains a white ash, the average composition of which is stated by Fleishmann and Schrodt to be: ^ A part of the phosphoric' anhydride of the ash is derived from the phosphorus of the ca sein. The sulphuric anhydride also comes from the oxidation of the milk proteins. If these acid constituents are deducted the bases in the ash are found to be in considerable excess. In the milk these bases are combined partly with the casein and partly with citric acid, a very small quantity of the latter being a normal constituent of cows' milk. The amount of ash does not, therefore, exactly represent the min eral matter originally present. The ash of nor mal milk is usually between 0.65 and 0.80 per cent, averaging about 0.73 per cent. The ash tends to vary with the proteins approximately in the proportion —Ash =0.38 + 1/10 Protein.
Nutritive Value and Place in the Diet.— From the above statements regarding the com position of milk one may conclude that it con tains proteins, fats, carbohydrate and salts in good quantitative relation to each other. The nature of the nutrients in milk also emphasizes its value as a food. Recent feeding experi ments comparing different proteins have shown milk albumin to have the highest nutritive value of any protein known, both for maintenance of grown animals and for supporting the growth of the young. Casein also has a very high nutritive efficiency and it is probably safe to say that the proteins of milk are of superior value in nutrition to those of any other known article of food. The fat of milk being in the form of an emulsion is more easily digested than ordinary food fats, and while the various fats after being digested and absorbed are of about equal value as sources of energy, yet milk fat and the butter made from it have been found to have a special value as food because of the presence therein of the recently discov ered fat soluble vitamine mentioned below. The sugar of milk is less likely than cane sugar, either to directly irritate the stomach or to undergo fermentation, and it is among the most readily available of foodstuffs, requiring only a single cleavage to bring it into form for ab sorption and utilization by the body. The pro portions of the different elements in the ash of milk make it an exceptionally valuable source of these inorganic foodstuffs, particu larly because of its high calcium content. In addition to the foodstuffs of known chemical i nature it has recently been found that there are required for normal nutrition two other substances or groups of substances both of which are furnished by milk. The one has
already been mentioned as occurring in the milk fat. It is referred to in recent literature as 'gat soluble vitamine or soluble The other essential foodstuff furnished by milk is soluble in water and therefore remains in the skim milk in butter-making or in the whey in cheese-making. It is referred to as the water soluble and as ewater soluble Milk is therefore the nearest approach to perfect food)) that we'have in any one commercially available article of diet.
On account of the richness of milk in all groups of foodstuffs, including those whose ex istence has only recently been recognized, the purchase of milk at ordinary prices is a much more economical investment than is commonly supposed. For families spending as much as 20 cents per person per day for food, milk at 10 cents a quart may be considered a more profitable investment than the average of the food purchased; and for those able to spend 30 to 40 cents per person per day for food the purchase of the highest grade of milk, even at a price of 15 to 20 cents a quart, is by no means extravagant The commonest defect of the dietaries of city families is the inadequate use of milk. Investigations under the auspices of the New York Association for Improving the Condition of the Poor have shown that city dietaries are more often deficient in calcium than in any other chemical element and that the use of more milk is the most effective way of remedying this defect and at the same time making the diet better balanced in other re spects and much better suited to the needs of growing children. In families where there are as many children as adults, at least as much money ought to be spent for milk as for meat.
Food Laws — Standards of Purity.— On account of the great importance of milk as food most of the States had laws regulating the sale of milk and established standards of com position for it even before the enactment of the general food laws. More attention has doubtless been given to the standard of purity for milk than for any other article of food. The official definition and standard of composition followed in the enforcement of the United States Food and Drugs Act and is most of the States is as follows: Milk is the fresh. clean. lacteal secretion obtained by the complete milking of one or more healthy cows, properly fed and kept, excluding that obtained within 15 days before and 10 days after calving, and contains not less than as per cent of solids-not-fat and not less than 3.25 per cent of milk fat.
In recent years much attention has also been given to the establishment of sanitary standards and the grading of milk on the basis of sani tary qualities. The grades and standards rec ommended by the National Commission on Milk Standards are as follows: RAW Mille of this class shall come from cows free from disease as determined by tuberculin tests and physical examinations by a qualified veterinarian, and shall be produced and handled by employees free from disease as cic,erminM by medical inspection of a qualified physician, wader sanitary conditions, such that the bacteria count shall not exceed 10,000 per cubic centimeter at the time of de livery to the consumer. It is recommended that dairies from which this supply is obtained shall score at least 80 OD the United States Bureau of Animal Industry score card.