Relation of Disease-Bacteria to Milk. 83 



the milk sufficiently so that their presence can be detected 

 by a physical examination. These facts which have been 

 experimentally determined, coupled with the numerous 

 -clinical cases on record, make a strong case against milk 

 serving as an agent in the dissemination of disease. 



Origin of pathogenic bacteria in milk. Disease-produc- 

 ing bacteria may be grouped with reference to their relation 

 toward milk into two classes, depending upon the manner 

 in which infection occurs: 



Class I. Disease-producing bacteria capable of being 

 transmitted directly from a diseased animal to man through 

 the medium of infected milk. 



Class II. Bacteria pathogenic for man but not for cattle 

 which are capable of thriving in milk after it is drawn from 

 the animal. 



In the first group the disease produced by the specific 

 organism must be common to both cattle and man. The 

 organism must live a parasitic life in the animal, develop- 

 ing in the udder, and so infect the milk supply. It may, 

 of course, happen that diseases toward which domestic ani- 

 mals alone are susceptible may be spread from one animal 

 to another in this way without affecting human beings. 



In the second group, the bacterial species lives a sapro- 

 phytic existence, growing in milk, if it happens to find its 

 way therein. In such cases milk indirectly serves as an 

 .agent in the dissemination of disease, by giving conditions 

 favorable to the growth of the disease germ. 



By far the most important of diseases that may be trans- 

 mitted directly from animal to man through a diseased 

 milk supply is tuberculosis, but in addition to this, foot 

 and mouth disease (aphthous fever in children), anthrax 

 and acute enteric troubles have also been traced to a sim- 

 ilar source of infection. 



