" Third: That the health officer is justified in ruling that large numbers of bacteria are a source of possible danger. and that milk containing large numbers of bacteria is to be classed as unwholesome, unless it can be shown that the bacteria present are of a harmless type, as for example, the lactic aad bacteria in buttermilk, or other especially soured milks." Pasteurization.— Since under ordinary con ditions it is not always possible to guard per fectly against the possible introduction of the germs of communicable disease into milk and since times and temperatures of heating milk, so as to ensure destruction of such pathogenic bacteria with exceedingly little, if any, injury to the milk itself, have now been thoroughly worked out, there is now practically unanimous agreement among those most interested in the subject that all milk, except that produced under extraordinarily good sanitary conditions, should be subjected to modern low temperature pasteurization before being used. In order to guard against injury to the antiscorbutic prop erties of the milk it should preferably be pas teurized at a temperature of only 140° to F. (60° to C.). Heating at this temper ature for 20 to 30 minutes is the best safeguard against distribution of disease through milk; and milk thus pasteurized and protected from subsequent contamination or deterioration may be used with confidence that it has been ren dered safe as regards pathogenic bacteria with out serious injury to any of the normal con stituents of the milk itself. Since there is a possibility that the antiscorbutic properties of milk may be injured to a slight extent by even low temperature pasteurization, it is advisable that infants and young children fed on pas teurized milk should be given orange juice or other food of known antiscorbutic property and suited to the age of the child.
Preservation of Milk produced under usual conditions contains large numbers of bacteria. At ordinary temperatures these multiply rapidly and soon cause such changes as to render the milk unsalable, if not unfit for use. Various preventive measures may be adopted, either to prevent bacteria from get ting into the milk, to check or control their growth or to destroy them entirely. Strict cleanliness and the use of sterilized utensils exclude a large proportion of the bacteria usu ally present in milk and greatly improve its keeping qualities. If such milk is protected from access of air and kept cold, it will remain sweet and fresh for at least two or three weeks without any other preservative measures. (The sanitary production and handling of milk are more fully described in the article: DAIRY INTERESTS, AMERICAN). In this respect the American dairy practice is much in advance of that of other countries, as was strikingly shown at the exhibit of dairy products at the Paris Exposition of 1900. Three dairies engaged in city milk supply, one in New York, one in New Jersey and one in Illinois, sent regular ship ments of fresh milk and cream to Paris throughout the summer. These products were
found to he sweet and sound when opened from 15 to 20 days after bottling, and it was only with great difficulty that European dairy experts could be convinced that nothing but and cold* had been used to pre serve them. No other country except France attempted to show natural milk and cream and the French exhibits were all sour on the second or third day.
It is evident that milk may be preserved much longer than is usually necessary by the observance of cleanliness to exclude bacteria as far as possible and the maintenance of a low temperature to retard the growth of those present.
Chemical Various sub stances have the power of preventing or re tarding the growth of bacteria. Those most often used to prevent milk from souring are boracic acid or borax, and formaldehyde. Much more rarely salicylates, chromates, fluo rides and other substances have been reported. Since milk often forms the sole food of infants and invalids the use of chemical preservatives is more objectionable in milk than in other foods and should be strictly prohibited, as is usually the case.
Milk is sometimes treated with carbonate or bicarbonate of soda which neutralizes the lac tic acid which would otherwise make the milk sour. These substances do not check the growth of bacteria but simply mask the results of their activity. By neutralizing the lactic acid they favor the growth of the bacteria which attack the proteins as well as those which affect principally the milk-sugar. Such milk, therefore, tends to become unwholesome more rapidly than milk to which nothing is added.
Methods of Analysis and Detection of The complete analysis of a sample of milk requires much time and elabo rate apparatus and is not practicable for others than trained chemists. The tests described be low are more easily performed and if carefully carried out will in many cases yield all the in formation required. Before taking a portion for any determination the milk to be tested should be thoroughly mixed by repeatedly pouring it from one vessel to another.
Determination of Since fat is both the most valuable and the most variable of the solids in milk, its determination is often re quired. This may be accomplished by the method devised by Dr. S. M. Babcock, of the Wisconsin Agricultural Experiment Station, and popularly known as the Babcock test. In making this test, a measured amount of milk is treated with about an equal volume of com mercial concentrated sulphuric acid which dis solves the other constituents, leaving the fat free in a heavy solution from which it is sepa rated by centrifugal force and collected in the graduated neck of the test bottle, where its vol ume is read off at once on the completion of the test. Complete directions are furnished with the testing outfit, which can be purchased for a few dollars from dealers in chemical appara tus or dairy supplies.