Milk is not easily digested by some persons. The tendency to costiveness caused by a milk diet can be largely overcome by the use of salt with the milk, or of some solid food, as toast or crackers, to prevent coagulation and the formation of masses resistant to the digestive fluids. Barley water and lime water in small amounts are also useful for assisting mechanically in the digestion of milk. Milk at ordinary prices is one of the cheapest foods that can be used.
[Illustration: FIG. 23.--DIRT IN A SAMPLE OF UNSANITARY MILK.]
102. Sanitary Condition of Milk.--Equally as important as composition is the sanitary condition or wholesomeness of milk. Milk is a food material which readily undergoes fermentation and is a medium for the distribution of germ diseases. The conditions under which it is produced and the way in which it is handled determine largely its sanitary value, and are of so much importance in relation to public health that during recent years city and state boards of health have introduced sanitary inspection and examination of milk along with the chemical tests for detecting its adulteration. Some of the more frequent causes of contaminated and unsound milk are: unhealthy animals, poor food and water, unsanitary surroundings of the animals, and lack of cleanliness and care in the handling and transporting of the milk. Outbreaks of typhoid and scarlet fevers and other germ diseases have frequently been traced to a contaminated milk supply.[37]
103. Certified Milk.--When milk is produced under the most sanitary conditions, the number of bacterial bodies per cubic centimeter is materially reduced. In order to supply high grade milk containing but few bacteria, special precautions are taken in the care of the animals, and in the feeding and milking, and all sources of contamination of the milk are eliminated as far as possible. Such milk, when sold in sterilized bottles, is commonly called "certified milk," indicating that its purity is guaranteed by the producer and that the number of bacteria per unit does not exceed a certain standard, as 8000 per cubic centimeter. Ordinary market milk contains upwards of 50,000.
104. Pasteurized Milk.--In order to destroy the activity of the bacterial organisms, milk is subjected to a temperature of 157° F. for ten minutes or longer, which process is known as pasteurization. When milk is heated to a temperature above 180°, it is sterilized. Below 157°, the albumin is not coagulated. By pasteurizing, milk is much improved from a sanitary point of view, and whenever the milk supply is of unknown purity, it should be pasteurized.[38] After the milk has been thus treated, the same care should be exercised in keeping it protected to prevent fresh inoculation or contamination, as though it were unpasteurized milk. For family use milk can be pasteurized in small amounts in the following way: Before receiving the milk, the receptacle should be thoroughly cleaned and sterilized with boiling water or dry heat, as in an oven. The milk is loosely covered and placed in a pan of water, a false bottom being in the pan so as to prevent unequal heating. The water surrounding the milk is gradually heated until a temperature of 159° F. is registered, and the milk is kept at this temperature for about ten minutes. It is then cooled and placed in the refrigerator.