In his relation to this problem each person must decide for himself. We do not cease to ride in the cars because there is danger here, nor do the innumerable accidents from bicycling deter us from this pleasure. Ought we to give up milk because of an occasional instance of disease? It might be possible to give advice to use milk freely, looking upon the danger as a slight one and one of the unavoidable dangers of living, but if such advice is given some one will instantly declare it bad advice. It might be possible to advise boiling all milk before drinking, and again some authority would say that this is unnecessary and bad. Personally, the author, though living in a small community, uses raw milk with perfect freedom, but would regard it as unwise to allow young children, especially infants, to use it in this way.
As already stated, the agitation over the milk supply is greater in Europe than in this country. While in England milk is used much as in this country, on the continent really little milk is drunk raw, and there is a growing demand for some means which shall deprive milk of the suspicions attached to it. This demand has been rapidly growing in recent years, and has resulted in the appearance of two new industries. These are the preparation of sterilized and Pasteurized milk. Neither of these industries has as yet developed much in the United States, although in our larger cities beginnings are being made along similar lines.
Sterilized milk has been used for many years. Long ago our doctors learned to recommend, for invalids, that milk should be boiled before drinking. This was done before the matter of its relation to bacteria was understood, and when physicians simply conceived that the boiling rendered the milk more digestible. From being used by invalids it came to be suggested in feeding infants, and then, after the relation of milk to possible disease germs had been understood, the general sterilization of milk was widely recommended. The process of sterilization of milk has not taken much of a hold upon the people of this country as yet, nor has it in England. In continental Europe, especially in northern countries, where the amount of tuberculosis is very large, it has made rapid headway, and now in most of the cities sterilized milk can be bought on the streets just as easily as ordinary milk.
In sterilizing milk as it is done in Europe the destruction of the disease germs is not the only purpose. An object of perhaps equal weight is to produce a milk that will keep. There are many circumstances where it is desirable to carry milk for long distances, and to lay in a supply to last many days or even weeks. Under these circumstances sterilization is resorted to, since it preserves the milk.
There are various methods of sterilizing milk. The simplest, and doubtless the most common, is simply the boiling of the milk. This can easily be done by any one at home, and is, beyond question, very widely resorted to. But where the sterilization is to be performed by a public-supply company, boiling is not satisfactory, since the milk, although it will keep some time, is not indefinitely preserved. The common method used is heating with superheated steam. The milk is placed in bottles of special device, holding about a pint or a quart, and are placed, hundreds at a time, in a large chamber which can be hermetically sealed and then filled with steam under pressure. Here the temperature rises to 102° to 106° C. (216° to 220° F.), and is retained here for some little time. This high heat is supposed to kill all the living bacteria that may be in the milk, even the resisting spores being commonly destroyed. While the milk is still in this apparatus, and before the chamber is opened, the bottles are sealed by a mechanical contrivance and then allowed to cool. After this they are taken out of the sterilizer, and are ready for distribution. The milk thus treated is sometimes pure white, although frequently it has acquired a brownish color, which is not enticing to one accustomed to ordinary milk. Moreover, it has a taste of cooked milk, which is to some people very unpleasant. But when the method is successful the milk contains no living bacteria, and may now be kept indefinitely without further change. It may be shipped to all parts of the world, and whenever opened it will be found still sweet. The process is evidently equivalent to the canning of fruit or meat, only more difficult because the milk commonly contains many resisting spores.
Such sterilized milk can be bought almost anywhere in Europe, and there is undoubtedly a growing demand for it. Where this or other sterilized milk is used it is claimed that very favorable results follow. Careful statistics have been collected as to the number of deaths among infants from diarrhœal diseases, and it is found that in some cities the deaths from infants fed upon raw milk are nearly three times as great as among those fed upon sterilized milk. Of course, no typhoid epidemics can ever be traced to such milk, and in general its use seems to meet with decided favor.
There are, however, some serious objections to this method of treating milk, which have been and probably will continue to be sufficient to prevent its wide extension. The first is that such milk appears to be slightly less digestible than raw milk. Over this matter, however, there has been and still is a great diversity of opinion, and many claim that there is really no difference in the digestibility. It is a matter of comparatively little importance, however, at least for adults and healthy children, for the sterilized milk can be digested, and the slight difference in ease of digestion probably has little significance unless it be for weakly individuals. Secondly, the taste of the sterilized milk is that of boiled milk, and this is rather unpleasant to most people. Probably a majority of our people, if called upon to drink sterilized milk or none at all, would prefer to give it up entirely. This is really an almost insurmountable obstacle to the wide extension of the use of sterilized milk, at least for the present generation. Those who have accustomed themselves to the taste of raw milk will not drink sterilized milk, and, if they do not dare to drink it raw, will not drink it at all. If infants are brought up on sterilized milk the next generation may look upon the matter differently, since the taste can be cultivated.
The third objection to sterilized milk is its cost, which pretty effectually prevents its wide use. Here is probably the real reason why the sterilized-milk industry has not extended more rapidly than it has. The cost of the milk that has been subjected to the treatment above described is considerably above that of ordinary milk, and the size of the pocketbook is commonly a matter outweighing, with most people, even matters of health. When raw milk can be purchased at half the price of sterilized milk, or even for a cent or two less, it will be purchased almost uniformly by the bulk of people, rather than the more expensive sterilized milk. Thus it happens that, in spite of the fact that sterilized milk can be purchased easily in most European cities, the business is not a large one. Probably not one quart of sterilized milk is sold to a hundred quarts of raw milk, even in cities where the business is best developed.
There are some who think that this method of treating milk is soon to be recognized as a necessity, and that it will be shortly regarded as improper to drink raw milk as it is to eat raw pork. But the business has grown rather slowly. Most people prefer to purchase their milk raw at a cheaper price and then boil it themselves, if they do not forget it. There is, moreover, one rather serious criticism that is made against this sterilized milk. Even with the high temperature that is used, it is impossible to be sure that all bacteria spores are destroyed. In most cases they are killed, but occasionally, and indeed not infrequently, a lot of milk will contain resisting spores that the heat does not destroy. These few spores that are left may become serious, far more so than the bacteria in raw milk. After sterilization they begin to grow, and, since this milk is very commonly kept for many days before it is used, these germs have a chance to become very abundant in the milk and to produce profound chemical changes therein, in some cases actually developing poisons. The changes that thus occur may be such as to escape notice with the eye, since they do not curdle the milk, and they may even fail to affect the taste of the milk. Such milk is to all appearances good, and would be given to infants without hesitation. If it did contain the injurious products thus referred to the results would be serious. Some bacteriologists are convinced that not a few cases of serious sickness have been produced in this way. When the milk is used shortly after the sterilization this matter is of no importance, since the bacteria spores grow slowly. But sterilized milk is supposed to keep indefinitely, and is therefore likely to be preserved some time before using, giving abundant opportunity for these spores to grow.
For these several reasons there is developing a different method of dealing with the problem. It is the well-known process of Pasteurization. But although the process has been known for several years, its application to the milk business on a large scale is quite new. Pasteurization consists in heating the milk to a temperature of only about 68° to 85° C. (165° to 185° F.), leaving it at this temperature for a short time, and then rapidly cooling. The length of time required depends upon the temperature used, being, of course, shortest for the higher temperature, but it varies from some two minutes to half an hour. This moderate heat does not necessarily produce the cooked taste nor, as we shall see, does it involve an expense which need raise the price. The temperature, however, is not sufficient to destroy all bacteria, and for this reason is looked upon with disfavor by those who feel that what is needed is an absolute destruction of all bacteria. The Germans, who like to do things thoroughly, do not take readily to Pasteurization, and there are others besides Germans who insist that this treatment does not make the milk safe. But if one is looking for practical possibilities rather than theoretical success, there is perhaps at present more to be said in favor of Pasteurization than sterilization.