Milk

MILK is the secretion of the mammary glands (mammae) of the large class, the Mammalia, of vertebrate animals that suckle their young. Those animals the milk of which is commonly con sumed by man are the cow, the goat and the sheep.

The average composition of milk, according to Richmond is shown in the following table.

But the rapid increase in the supply of milk, and the growing facilities for its distribution provided by the development of motor transport, made it more and more difficult to maintain producers' prices; and by 1933 the whole condition of the milk trade was verging on chaos.

The pressing need for complete organization led the milk pro ducers in 1933 to set up the Milk Marketing Board for the pur pose of fixing the price at a level adequate to the producers, controlling distribution, and preventing overlapping and waste.

Milk Classification.

Various "clean milk" movements have resulted, in England, in an optional system of grading milk with a sufficiently high degree of bacterial purity. The following stand ards are laid down under licence granted by or under the authority of the Ministry of Health:— While the lactose and mineral salts are in true solution (see SOLUTIONS) the proteins, caseinogen and lactalbumin, are present in colloidal solution, with which fat is intimately mixed in the form of an emulsion or suspension of globules.

Milk is a complete food, containing as it does protein, fat, car bohydrates, mineral constituents, and water. Though deficient or lacking in certain metallic elements believed essential for normal adult health, the milk of any species is an adequate diet for the very young of that species in all respects, including its contents of vitamines (q.v.). On the other hand, it may not be equally satis

factory for the young of another species. Thus cow's milk is not always an absolute source of vitamine C for human infants. Nor mally cow's milk if produced under proper conditions is an ade quate source of vitamines A and B, and a reasonably good source of C and D. Its content of vitamine E is probably low.

Variation in Composition.

The specific effects of different circumstances on the yield and chemical composition of milk are frequently dealt with in the reports on the experimental work carried out by the various agricultural colleges. According to Mackintosh the naturally occurring conditions which influence the yield and quality of milk can be summarized as follows:—I. Breed of Cow. 2. Individuality of Cow. 3. Period of Lactation. 4. Inter val between milkings. 5. Efficiency of the milker. 6. Age of the Cow. 7. Climate and weather conditions. 8. Health of the Cow. 9. Kind and quality of food.

Under the Food and Drugs Act milk (other than skimmed, separated or condensed milk) must contain not less than 3 per cent. of milk fat and 8.5 per cent. "solids not fat," until the con trary is proved. Skimmed or separated milk should contain not less than 8.7 per cent. total solids.

The

addition of preservatives or of colouring matter is illegal.