314 DISTRIBUTION OF BACTERIA 



The Disease-producing Bacteria in Milk. A third group of 

 bacteria which unfortunately are sometimes found in milk are 

 those capable of producing human diseases. Some of these 

 bacteria are derived directly from the cow, as Bact. tubercu- 

 losis, for example. In other cases the infectious agent enters 

 after the milk is drawn. From the standpoint of public 

 health this group is far more important than any other group 

 of bacteria found in milk. In the case of the bacteria which 

 are derived directly from the animal it would seem possible 

 to protect the public when they are sufficiently aroused to de- 

 mand protection. In those cases where the disease-producing 

 bacteria enter after the milk is drawn, the problem is more 

 difficult, because it seems quite impossible to detect mild 

 cases of such diseases as typhoid fever, diphtheria, and scar- 

 let fever in those that handle milk. It seems likely that 

 occasional epidemics may occur for a good many years, al- 

 though- rigid inspection could quickly bring these epidemics 

 to a minimum. 



Disease Bacteria derived directly from the Animal. 

 Tuberculosis is very common among dairy cattle. It is also 

 the most common disease of man, and that it may be trans- 

 mitted from cattle to man seems beyond doubt. When 

 milk from tuberculous cows is inoculated into guinea pigs, the 

 disease is produced, as a number of investigators have found 

 long ago. Russell, for example, found that i cc. of milk 

 killed a rabbit. Bact. tuberculosis is present in milk not only 

 when there is an apparent disease of the udder, but also when 



