at one temperature while others multiply rapidly at another. As a rule the bacteria contained in milk increase prodigiously at a temperature of from 70° to 100° F., while their growth is retarded at 50° F. or under, which is or should be the temperature of the ordinary household refrigerator. For example, two samples of milk containing the same number of bacteria are maintained, one at a temperature of 50° and the other at 70°. At the end of 24 hours the first sample will contain at the most only five or six times the original number of bacteria while the second sample will show five or six thousand times the original number. A change of only a few degrees of temperature will thus bring about an enormous difference in the bacterial life and may convert a milk which is relatively safe for consumption into one which is extremely dangerous. The importance of this fact should of course be apparent to every person concerned in the handling of milk. The maintenance of all supplies at a temperature where bacterial development is retarded is absolutely essential if a dependable milk is to be obtained. Particularly is this true in the summer season when natural temperatures are high.

A fact of extreme importance relating to the influence of heat upon bacteria is the temperature at which organisms are killed. When milk is exposed to a temperature of 145° F. and is held at that point for 30 minutes all disease-producing organisms are destroyed; if the supply is then immediately chilled further multiplication of the remaining germs is temporarily inhibited. As we shall later see, this is taken advantage of in the process known as pasteurization. Time is another factor which greatly influences the development of bacteria, the two conditions, time and temperature, working hand in hand. Milk freshly drawn from healthy cows contains relatively few organisms, but after a lapse of several hours, even when the sanitary conditions are of the best and the temperature is low some multiplication occurs. Ordinarily milk reaches the consumer within 48 hours after it is produced; if this period is lengthened the quality will be proportionately endangered, and this notwithstanding the proper chilling and handling of the supply. Fresh milk is therefore always to be considered preferable to that which is not recently drawn, although freshness is by no means proof of purity.

The Number of Bacteria in Milk.

One of the means used for determining the purity of a milk is the estimation of the number of bacteria present. This is done by counting, a procedure which is now common in all health laboratories. The bacterial count of fresh milk is a measure merely of the cleanliness of a particular supply and the cleanliness is to a degree a

measure of the safety. It would, of course, be more desirable if we could determine the safety of a given sample directly without regard to the cleanliness, for, as we know, not all dirt is dangerous, neither are all forms of bacteria harmful. In the present state of our knowledge, however, this is impossible. Therefore in order to avoid dangerous dirt it is necessary to avoid all dirt. Milk with a low bacterial count is considered safest and best, while that with a high count may be actually dangerous.

As stated, the number of bacteria in milk just from the cow is always in proportion to the cleanliness, but in market milk the temperature at which the product has been maintained, the amount of handling it has undergone, and the age, are also factors in determining the number of bacteria present. If the supply is fresh and has been obtained with strict conformity with the rules of cleanliness, if the containers have been properly cleansed, and if exposure to dust and dirt has been kept at a minimum, the bacterial count will be low. On the other hand milk which has been shipped for long distances without proper chilling, that which has come in contact with nonsterile containers, or supplies which have been carelessly handled at any part of their journey from producer to consumer, will show a high count.

In conformity with the knowledge that milk containing large numbers of bacteria is due to carelessness in production or handling and may be harmful, boards of health have deemed it necessary, as a measure of safety, to limit the number of bacteria which milk offered for sale may contain, and to make accurate counts at stated intervals. to see that this limit is not exceeded.

Just what limit is to be placed upon the number of bacteria in milk is a matter for determination by the health authorities, after due consideration of the difficulties which the producers and purveyors may encounter. A low count for a city would be a high count for a country milk. The climate, the season of the year, transportation facilities and availability of ice are all matters to be considered in fixing a standard. In small communities where milk is produced within a few miles of the point of delivery bacterial counts of 100,000 may be considered excessive, whereas in large cities receiving their supplies from places perhaps a hundred or more miles distant counts on raw milk below 100,000 are rare.

DISEASES WHICH MAY BE CONVEYED BY MILK.

Outbreaks of disease brought about by milk usually present certain distinguishing characteristics which serve to determine their source. For the most part the disease is confined to the milk route of a certain dealer: that is, to families using a particular supply. Instead of the

epidemic developing gradually and the number of cases increasing from day to day, it comes on suddenly, the maximum number of cases frequently being recorded at the very onset. The subsidence may be nearly as rapid. Only those who have actually used the milk or its products are attacked. People in the better walks of life are if anything more subject to the disease than those in poorer circumstances, while women and children are more frequently made ill than others, this because these classes are more apt to be milk consumers. Upon the closing of the dairy or the pasteurization of the supply the epidemic is immediately terminated. These facts, in themselves, furnish conclusive proof of the source of the disease, but in many instances the person responsible for the infection can be identified by the health officer and at times the infectious agent can even be recovered from the milk.

Milk derived from animals which are themselves suffering from disease is unfit for consumption. Supplies obtained from cows afflicted with anthrax, tuberculosis, lumpy jaw, or other infections should not be used. However, milk which has its origin in perfectly healthy stock may to an even greater extent be responsible for illness than that from diseased stock, a fact which we are quite too slow to appreciate.

Typhoid fever.-One of the most fatal diseases conveyed by milk is typhoid fever. This is an infection peculiar to man due to a specific germ, the typhoid bacillus, which gains entrance to the system through the mouth, the poisons generated during its multiplication producing the characteristic symptoms of the disease. Every case of typhoid fever arises from a preexisting case, and milk only serves as one of the means of transference of the bacilli from infected persons to those who are well, water and other foods likewise frequently conveying the infection. The contamination in all cases is accidental. Whenever typhoid organisms obtain access to milk they increase rapidly in number, particularly if the temperature is favorable, so that within a few hours they may contaminate an exceedingly large supply, thus distributing the infection far and wide. The rapid growth of bacilli which follows contamination with typhoid organisms produces no recognizable changes, and a fluid which is perfectly normal in taste, sweetness, and appearance may be teeming with organisms of this nature.

The typhoid bacillus is killed by heat, but is quite resistant to cold, hence the freezing of milk and cream affords no protection to consumers, epidemics of typhoid having frequently been traced to infected ice cream. Butter, cheese, and other dairy products may not be free from danger, although it is considered that they are much less apt to convey the infection than milk itself.

The organism causing typhoid fever gains entrance to milk in various ways, and contamination may occur at any point on the route from the farm to the consumer. Infection most frequently takes place, however, at the dairy. The pollution is not always directthat is, it may be transferred by secondary objects, so that it is entirely unnecessary for a person actually ill of typhoid fever to come in direct contact with a milk supply for contamination to be brought about. The improper disposal of human excreta on dairy farms strongly predisposes to the development of typhoid infection in milk and is a condition never to be tolerated. Flies and other insects having access to unscreened and unprotected privies may travel to the stable or milk house carrying with them the contagion of the disease; it should not be forgotten that milk may also be befouled in this identical manner both in the home and at places where it is offered for sale. Another source of contamination at the dairy is polluted water. Seepage from privies and outhouses may obtain entrance to wells, a condition not at all uncommon in country districts, and the polluted water from these sources may be used in washing the milk pails or cans, thereby transferring the typhoid germ directly to the milk.

The occurrence of a case of typhoid fever among the employees or members of a dairyman's household, or of any other person engaged in the handling of milk, is always a matter of grave concern and calls for the strictest regulation on the part of the health department. Persons engaged in caring for such cases may contaminate the hands with the infection, thus polluting the supply. Frequently those who are in the early stages of typhoid fever are able to be about, attending to their daily duties, and under these circumstances they constitute an especially dangerous class. The most insidious agent of all, however, is the typhoid carrier, the person who has recovered from the disease but who continues to discharge bacilli in his excretions. Such a one may actually be working as a milker or engaged even in the care of the supply, thus affording, if strict cleanliness is not practiced, the greatest opportunity for infection. With these facts in view one can easily understand how important it is for a health department to possess knowledge of the occurrence of every case of infectious disease wherever milk is produced or handled.

Whenever typhoid fever develops in a community in epidemic form milk contamination should be considered; in fact, it should be a matter of consideration when the disease is not epidemic, as many of the scattered cases are doubtless due to this cause, although they are more difficult to trace to their source than those affecting large numbers. In all instances of this character the milk should be pasteurized, boiled, or its use altogether discontinued, the epidemic at once ceasing when this is done.

As a rule milk epidemics of typhoid fever present characteristic features which are highly significant to the trained sanitarian. Often the investigator is able to trace the contagion to the dairy concerned and in many instances to the very person who constitutes the source of the infection and from whom the bacilli are being derived. In nearly all instances not only is it found that some person suffering from the infection is living on the premises but that there has been in addition gross carelessness in the methods of handling the supply. Cleanliness is therefore a most important element in safeguarding against this far too common infection.

Malta fever.-A second disease conveyed by milk but one which is merely of academic interest to residents of most sections of this country is Mediterranean fever (Malta fever). As the name indicates Mediterranean fever is so called because of its occurrence in the countries bordering the Mediterranean Sea, but foreign countries, including Mexico and the United States, have been invaded by the infection. The disease primarily affects goats, the chief source of the milk supply in many European countries, and is due to a specific microorganism. When taken into the system the organism gives rise to fever continuing over many weeks, debility, rheumatic pains, and swelling of the joints, the infection usually terminating, however, in recovery after a considerable period of invalidism. The infectious agent is usually, although not invariably, conveyed by milk. In a number of Mediterranean cities strict regulations are in force forbidding the sale of unboiled milk, and in consequence the disease has almost entirely disappeared in these places. In the United States a small area of infection exists in western Texas and New Mexico.

Scarlet fever.-It is considered that scarlet fever is quite frequently conveyed by milk. Numerous epidemics have been reported where practically all of the cases occurred along the route of a single dealer, the epidemics declining rapidly upon pasteurization of the milk supply. However, outbreaks of scarlet fever traced to this cause are much less common than outbreaks of typhoid fever. Perhaps one reason for this is that they are more difficult to trace to their source. The germ causing scarlet fever has never been discovered, but it is believed to exist in the secretions of the mouth and throat and one can readily understand how by careless coughing or sneezing on the part of a milker convalescent from or in the early stages of the disease the infectious agent might gain access to the milk. Some investigators have thought that the infection is at times derived from diseased cows, and there is no doubt whatever that animals suffering from inflamed udders may produce a condition in man at least simulating scarlet fever. Probably one reason why milk-borne epidemics of scarlet fever are not more common is be