636 POPULAR SCIENCE MONTHLY. 



results would be serious. Some bacteriologists are convinced that 

 not a few cases of serious sickness have been produced in this waj. 

 AVlien the milk is used shortly after the sterilization this matter is 

 of no importance, since the bacteria spores grow slowly. But ster- 

 ilized milk is supposed to keep indefinitely, and is therefore likely 

 to be preserved some time before using, giving abundant oppor- 

 tunity 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 Pas- 

 teurization. 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 neces- 

 sarily produce the cooked taste nor, as we shall see, does it involve 

 an expense which need raise the price. The temperature, how- 

 ever, 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 pres- 

 ent more to be said in favor of Pasteurization than sterilization. 



Pasteurization is found to be sufficient to destroy all the strictly 

 pathogenic bacteria that are likely to be in milk. The germs of 

 diphtheria and typhoid are killed, and even the tubercle bacillus 

 is rendered innocuous by a few moments at a temperature of 75° 

 C. The resisting spores above mentioned are of course not de- 

 stroyed, and many other bacteria are left uninjured. But the bac- 

 teria which escape the heat are not strictly pathogenic, and do not 

 grow in the body. If they produce any injury to the drinker it is 

 because they grow in the milk and produce injurious chemical prod- 

 ucts there. They are only dangerous, tlierefore, after they have 

 had an opportunity to grow in the milk for some time. This op- 

 portunity they do have, as we have seen, in sterilized milk, but they 

 do not have the opportunity in Pasteurized milk. Pasteurized 

 milk is not designed for keeping, and those who use it know that 

 while the strictly pathogenic bacteria are killed the milk will not 

 keep. It will remain sweet a little longer than raw milk, but it 

 must be used at once. It must be treated just like fresh milk. 



