William H. Park and L. Emmett Holt analysed the milk bought in stores in the tenement districts in New York city, and its effect upon infant feeding. Some of their conclusions follow: In winter the average number of non-specific bacteria present in store milk is 750,000 per cc, a number which does not appear to be harmful. In summer over 1,000,000 bacteria per cc. of milk are always harmful to young infants, and the number may reach several hundred millions per cc. More than 139 varieties of bacteria were represented in the various samples of milk, no one of which appeared to be especially related to the summer diarrhoeas of infancy. After the first year of life the bacteria of milk seemed to produce very little disturbance in children unless present in enormous excess.

Milk carelessly transported promptly absorbs germs from the air or from unclean receptacles, and it is an excellent culture medium for rapid growth of such germs as those of tuberculosis, scarlatina, diphtheria, and typhoid fever, which may gain access to it in that manner. When local epidemics of such diseases break out, there should always be a thorough investigation of the sources of milk supply, and a bacteriological examination of the milk itself should be instituted. Many persons imagine that a chemical analysis is sufficient, but this is useless for detection of disease germs.

George M. Kober reported 330 outbreaks of infectious diseases of various kinds due to milk infection, and which had been recorded prior to 1901. Such epidemics are more common in England than in America, and least often appear in continental Europe, owing to the comparative in frequency with which raw milk is drunk there by both infants and adults.

Severe epidemics of typhoid fever have of late years been attributed to infected milk by H. E. Smith, at Waterbury, Conn.; by L. H. Taylor, at Wilkesbarre, Pa.; and by Littlejohn, who traced the origin of sixty-three cases to one dairy. Fourteen cases of typhoid fever occuring in East Barrington, N. H., in 1896, were traced to the eating of ice-cream contaminated by a milkman who had continued milking while himself suffering from the fever. No one who is nursing a case of typhoid or scarlet fever or diphtheria, or who in any way handles the discharges or clothing of such patients, should be allowed to touch milk or milk receptacles, much less to milk a cow.

Typhoid bacilli have also been proved capable of living in butter.

At Brewster, N. Y., Miller reported twenty-four cases of scarlatina which occurred among those who drank the milk supplied by one dairyman while his daughter had scarlet fever. The disease was not otherwise prevalent in the town at the time.

E. Hart reported at the Seventh International Medical Congress a series of epidemics in England the origin of which he had traced to milk. Of these, fifty were of typhoid fever, fourteen of scarlatina, and seven of diphtheria.

The diphtheria bacillus has not thus far been proved to be transmitted direct from the cow to man, but cows inoculated under the shoulder with diphtheritic microbes exhibit the germs in the milk after developing local lesions of the udders. Those epidemics of diphtheria the spread of which has been attributed to milk have probably been due to contamination through the handling of the milk by milkers or dairymen having the disease themselves or who have been in close contact with it. In this country Goodwin and W. H. Stillwin have both reported such epidemics occurring in Michigan in 1879. W. J. Howard, Jr., studied an epidemic of 100 cases in 49 houses in Ashtabula, Ohio, in 1894, which he is confident was referable to a milk supply delivered by boys who had severe angina at the time, although the bacillus diphtheriae was not found in their throats. The New York Health Board reported the discovery of the germs in cheese made by a milkman in whose family diphtheria was present.

A mould, the Oidium lactis, or penicillium, and the Bacterium cyanogenum are germs which produce a blue colour in milk and sour it. The mould also grows upon cream cheese. This colour appears first upon the surface if the milk be not agitated, and it differs from the uniform blue imparted by adulteration with water, or by poisonous plants, drugs, etc. Milk thus affected is irritant, and may cause febrile gastritis, stomatitis, or diarrhoea.

Milk is coloured lemon yellow by the Bacterium synxanthum (Ehrenberg), and red by chromogenic fungi.

The fungi and germs themselves do not impart the colours, but develop various anilines - aniline blue, fuchsin, etc. - from the casein (Schröter).

"Clouty cream " is produced by germ action.

5. There are ten different varieties of bacteria which are capable of inciting lactic-acid fermentation of the milk sugar (Leeds), all of which cause the milk to "sour " and curdle, and some, but not all, simultaneously develop carbonic acid and alcohol. A large proportion of the bacteria of milk rises with the cream to the surface (Freeman). Milk may be really decomposing although it has not yet coagulated.

The first process, that of the formation of lactic acid, is a preliminary to the normal digestion of milk, but the second is abnormal and interferes with it. The sour milk curd may be redissolved by neutralisation with alkalies.

The Bacillus acidi lactici may sour the milk before it is ingested, or, like many germs, their action may not be apparent before swallowing the milk, but it begins immediately thereafter in the stomach.

Good, clean, uncontaminated milk should keep fresh, exposed in a clean room at the ordinary temperature of 68° F. for forty-eight hours without souring and coagulating. But if the air is much warmer, or if the milk is tainted in any manner, it will sour in a few hours. Boiled milk keeps fresh rather more than half as long again as fresh milk.

6. The absorbent power of milk is strong, and it may acquire a strong odour from substances kept in its vicinity. It may acquire a bad flavour at the same time, or may have the odour alone.

If left in a refrigerator with stale cheese, ham, onions, decomposing meat, etc., it soon becomes spoiled in this manner. Milk easily absorbs the odour of tobacco, camphor, or of turpentine from fresh paint, and, in fact, the odour of almost any volatile substance. It should never be left exposed in the sick-chamber or in a bathroom, or near a waste pipe.