Milk is not only the most perfect human food but is likewise an unsurpassed nutrient medium for the growth of bacteria. Hence it is very liable to become unwholesome through the agency of microorganisms unless it is properly handled. In hot countries and among pastoral peoples who live under primitive conditions the practice is to promptly sour all milk by permitting a vigorous growth of certain races of lactic acid-producing bacteria in it. This protects the milk against proteolytic organisms which produce unwholesome decomposition products, because the rise of acidity is so rapid that all forms other than the acid-forming organisms and certain yeasts are killed or their growth inhibited. Sour milk is a highly wholesome food, and is used in enormous quantities in Asia, Arabia, the Balkan States, Northern Africa and in the grazing sections of Abyssinia. Wherever it is used in liberal amounts as human food, the people are of exceptional physical perfection. This will be further discussed later.

The number of bacteria in milk depends upon the temperature and age and the amount of dirt which is allowed to contaminate it. In America it is the custom to market liquid milk either raw or pasteurized. In order that this may be done in a satisfactory manner great care must be exercised in respect to cleanliness of cows and of milkers and of utensils; and refrigeration must be immediate and effective and delivery prompt. There has been steady progress in the supervision of the milk supply of cities in recent years and American cities have the most wholesome milk supplies in the world. All city milk supplies should be pasteurized. This is effected by heating the milk during thirty minutes to a temperature of 145 degrees, followed by prompt cooling and bottling in sterile containers. This prevents the spread of typhoid fever, scarlet fever, tuberculosis and other diseases which are sometimes milk borne.

Bacteria in milk are related to infant mortality. Children fed clean milk with few bacteria have a lower death rate than those who take milk with high bacterial counts. Many organisms which are relatively harmless to adults may cause diarrhea in infants and young children, or at least set up intestinal inflammation.

161. City Milk Supply Should Be Rigidly Inspected

The desirability of thorough control of a city milk supply through the agency of the health department has been fully justified by the results. Bacterial counts should be made regularly of market milk, (1) as an indicator of the care exercised in keeping healthy cows and in exercising cleanliness on the farm, refrigeration and promptness of delivery; (2) as a basis of condemning milk which is unwholesome because containing dirt, filth, or decomposed materials. Dairy inspection has come to be a well recognized method of insuring a wholesome milk supply.