Quart mixed market milk.

Bottle immersed in water 4 inches, 5 inches out.

Cream line very distinct from long standing.

The bottom milk hotter than the top, probably on account of heavy viscid cream on top that did not circulate.

COMMERCIAL PASTEURIZATION.

The commercial pasteurization of milk leaves much to be desired, but although it is not always thoroughly carried out, it is by no means a fraud. With a little sanitary supervision on the part of health officers and education on the part of those in charge the process may be made efficient.

Commercial pasteurizers are popular with dairymen, not because of the public health aspect, but on account of the economic advantages in improving the keeping qualities of the milk. It is estimated that the expense of a pasteurizer would be paid for in the course of about a year. This estimate is based mainly on the saving of losses from sour milk. The cost of pasteurization is about one-tenth to one-half cent a quart.

In order to satisfy public health requirements pasteurizers must be efficient in operation, permitting a definite quantity of milk to be heated to a definite temperature for a definite time (Russell). They must be easy of control, the milk must be heated uniformly throughout, the apparatus must be simple in construction, easily cleaned, economical in use, and arranged to safeguard against reinfection of the milk. Finally, provision must be made for rapid cooling. Given an apparatus of proper construction more depends upon the intelligence and care with which it is run than upon the machine. No pasteurizer is automatic. For instance, I have found that the milk pasteurized in a standard machine contained many more bacterial

after the process than before. This was not the fault of the machine, but due to ignorance and uncleanliness.

The following figures show the efficiency of a commercial pasteurizer operated under intelligent though not skilled supervision:

The above figures were obtained from a type of machine known as a" Flash pasteurizer," in which the milk is heated momentarily at 73° to 74° C.

The pasteurization of milk is such an important public health measure that it should be under the immediate and constant supervision of the health officer. The milk should be heated a definite temperature for a definite time and then promptly cooled, and properly labeled.

RÉSUMÉ ADVANTAGES AND DISADVANTAGES.

Pasteurization saves lives and prevents sickness. Weighing against this great merit we have certain disadvantages connected with the heating of milk. That there are two sides to the question may be judged from the fact that those who have given the matter careful consideration come to diametrically opposite conclusions. From a theoretical standpoint some believe pasteurization to be an unsatisfactory and very feeble way out of a very difficult situation. From a practical standpoint, others find in pasteurization our only practicable safeguard, at least until the general supply consists of good, clean, fresh milk.

One of the chief objections to pasteurization is that it promotes carelessness and discourages the efforts to produce clean milk. It is believed that the general adoption of pasteurization will set back improvements at the source of supply and encourage dirty habits. It will cause the farmers and those who handle the milk to believe that it is unnecessary to be quite so particular, as the dirt that gets into the milk is going to be cooked and made harmless. It is not proposed that pasteurization shall take the place of inspection and improvements in dairy methods. To insure the public a pure and

safe milk supply should be regarded as one of the most important. duties of the health officer. Whether pasteurization is adopted by a city for its general milk supply or not, no milk should be accepted that does not comply with certain reasonable chemical and bacteriological standards. This would aid the inspectors in enforcing good dairy methods. Pasteurization then must not be used as an excuse to bolster up milk unfit for home consumption. To insure this end, the health officer should have authority to condemn and destroy bad milk, whether or not pasteurization is practiced.

To obtain a good milk supply involves not only an expensive system of inspection and surveillance from the farm to the consumer, but intelligence and a high degree of technical skill on the part of the producer and all others who handle the milk.

We can scarcely conceive of an inspection so thorough and constant as to prevent milk occasionally becoming contaminated with the germs of typhoid, diphtheria, scarlet fever, dysentary, tuberculosis,

etc.

If our drinking water is defiled at its source we boil or filter it. It would be much better to prevent its contamination. The same is true of milk. We prefer pure milk, but so long as we can not obtain it we must purify what we get. The situation may well be illustrated by the attitude of an eminent sanitarian in New York, who in his writing and public addresses discourages pasteurization, because theoretically it does not reach the source of the evil and is not as good in the end as purification of the milk supply through efficient inspection. However, when this same sanitarian is consulted by a large wholesale dealer of New York, who handles many thousands of quarts of more or less old dirty milk a day, he is confronted by a condition, not a theory, and advises pasteurization.

There is a prevalent impression that the pasteurization of milk improves that important article of diet. Heating does not render milk better in any way as a food. All it does is to destroy certain bacteria and some of their toxic products. It checks certain processes of fermentation and putrefaction, thus rendering the milk safer. On the other hand the evidence seems clear that the pasteurization of milk at 60° C. for twenty minutes does not appreciably deteriorate its quality or lessen its food value.

Pasteurization has been accused of possessing the great disadvantage of inducing scurvy and rickets. It is generally believed that highly heated milk is a contributive factor in the etiology of scurvy. There is certainly no evidence to show that low temperature pasteurization such as is now recommended ever in itself induces scurvy. Thousands of children have been raised upon heated milk without the production of this disease, which is comparatively rare, especially in

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countries such as Germany and France, where the artificial feeding with heated milk is most popular. Scurvy is preventable and amenable to treatment. Rickets results from defective alimentation and improper hygiene and can not be laid at the door of pasteurization.

Comparative observations upon infants under the same conditions show that they flourish quite as well upon heated milk as upon raw milk. Laboratory experiments as well as clinical observations coincide with the view that heated milk is quite as digestible as raw milk. In fact, it is now claimed to be more so. Metabolism experiments indicate that the utilization of calcium and iron in the body is more complete in children fed upon boiled cow's milk than in those fed upon raw cow's milk.

One of the great objections to the pasteurization of milk is that it devitalizes it. If milk contains "life" it has probably lost the last vestige of it after it is from twenty-four to forty-eight hours old and kept under such conditions that it contains myriads of bacteria. It has been shown that heating milk to 60° C. for twenty minutes, while it kills the pathogenic organisms, does not seriously affect the enzymes, and the enzymes are the nearest approach to "life" with which we are familiar in milk. The germicidal properties of milk are not seriously injured at 60° C.

Another objection frequently urged against pasteurization is that some of the bacterial toxins are not killed at the ordinary temperatures used. We do not even know the nature of these poisonous products in milk, much less their thermal death points. The true bacterial toxins are destroyed by heating to a temperature of 60° C. for twenty minutes. It must be remembered that if milk contains bacterial toxins not destroyed by pasteurization it will contain these same poisons if the milk is consumed raw. In fact the heating of the milk prevents the further formation of such injurious substances.

Pasteurization results in the destruction of the ordinary acidproducing bacteria, nature's danger signal of old milk. The heating interferes with the souring process, so that fermentation of another and perhaps more serious nature may take place without the knowledge of the consumer. It has been shown that certain resistant sporebearing bacteria have the property of peptonizing the albumens in milk. These bacteria survive the process of pasteurization, and are thus given a free field for growth, whereas in the raw milk these bacteria are largely held in check by the growth of the lactic acid forming organisms. This view started with the work of Flügge and has gradually lost ground for lack of clinical and laboratory confirmation. For instance, Park and Holt found that a few cases of acute indigestion immediately followed the use of pasteurized milk more than thirty-six hours old. Samples of such milk were found to