766 THE POPULAR SCIENCE MONTHLY. 



has been produced under the influence of different species of bac- 

 teria. The souring of milk is therefore not a simple or a uniform 

 phenomenon. While it is always the effect of bacteria growth, we 

 recognize many varieties of souring corresponding to the variety 

 of bacteria most abundant in the milk before souring. All this 

 makes little difference to the consumer ; in any case the milk is 

 ruined for his purposes, and he is more concerned in preventing 

 such troubles completely than in learning their variety. A rem- 

 edy seems simple enough. When we have once learned that the 

 whole trouble is caused by bacteria, we see that it is only neces- 

 sary to keep these organisms out in order to preserve the milk 

 pure and sweet. 



From the standpoint of public health also the desirability of 

 freeing milk from these organisms is becoming every day more 

 apparent. It is true that the vast majority of the bacteria in milk 

 are perfectly harmless to the healthy person, even when swallowed 

 in such numbers as above indicated. But, at the same time, it not 

 infrequently happens that disease-germs get into the milk and, 

 finding there a suitable medium for growth, multiply rapidly. 

 They are then served out to all the patrons supplied with the 

 milk. Typhoid fever is certainly disseminated by means of the 

 milk-supply, and there is a growing conviction that the fatal 

 tuberculosis owes much of its prevalence to milk from diseased 

 cows. Other epidemics have also been traced to the same source. 



Even if no definite disease-germ chances to be present in the 

 milk, the vast number of harmless forms may render the milk 

 dangerous to all having weak or sensitive digestive organs ; for 

 they produce considerable lactic acid, and every one knows that 

 acid is injurious in the food of infants and invalids. The pres- 

 ence of lactic acid is probably a less serious matter than the pres- 

 ence of certain decomposition products which are formed by the 

 same bacteria. These are directly poisonous, and, although they 

 are present in such small quantities that they have no effect on 

 the healthy person, they may be injurious to one whose digestive 

 organs are in a sensitive condition. For a long time doctors have 

 recognized that boiled milk is a safer food for invalids than raw 

 milk, supposing, however, the explanation to be that the cooking 

 renders it more easily digested, just as it does other foods. Recent 

 experiments have shown us that this is not true. On the con- 

 trary, boiled milk is less easily digested and absorbed by the 

 system than raw milk. The real reason for the greater safety 

 in drinking boiled milk lies in the fact that it is thus deprived 

 of the disturbing action of the millions of bacteria ordinarily 

 present. 



To keep bacteria out of milk is a practical impossibility. 

 Their presence in such quantities in all places renders their access 



