Il6 MILK BACTERIA AND HEALTH. 



It may seem somewhat strange that it is not positively 

 known whether milk is a source of tuberculosis in mankind. 

 The reason is the difficulty of getting direct evidence. The 

 direct experimental evidence of feeding men with highly 

 tuberculous milk is hardly feasible. To determine whether 

 any individual case of tuberculosis is due to milk is prac- 

 tically impossible. The disease is one of very slow progress 

 and is not recognized until after it has existed in the indivi- 

 dual for some time. When it is recognized that a person has 

 the disease it is practically impossible to determine its source. 

 It is known that all persons are subject to tuberculous 

 infection from various sources, and that they are liable 

 at any time to be exposed to the infection by breathing. If, 

 therefore, a person develops the disease it is quite impossible 

 to determine whether the disease came from breathing con- 

 taminated air or from using as food milk which contained 

 tuberculous material. In a few instances cases of tuber- 

 culosis have developed in a family and subsequently it has 

 been learned that the family has been using as food milk 

 from a tuberculous cow. While this is presumptive evidence 

 that the cow may possibly have been the source of the disease 

 it is by no means demonstrative, for other chances of infec- 

 tion are abundant, and there are thousands of cases of 

 families using milk infected with tubercle bacilli without any 

 evidence of tuberculosis developing. As a result of these 

 facts, the conclusion that milk is a means of distributing 

 tuberculosis rests upon indirect and uncertain evidence. 



There is no practical method of protecting the public milk 

 supply from the presence of the tuberculosis bacillus. It is 

 possible, by microscopic means, to detect the presence of the 

 bacilli in milk, but the process is so slow and so uncertain 

 that it is quite impracticable to apply it generally to market 

 milk. It is, also, impossible to tell by a physical examination 

 of a cow whether her milk will be contaminated with tubercle 

 bacilli or not. If she has the disease in her udder the con- 



