DISEASES CAUSED BY INFECTED MILK 97 



culosis is therefore spread, not alone from cow to man, but 

 from cow to cow, from cow to hog, etc. 



How frequently does milk contain tubercle bacilli ? Ordin- 

 ary market milk so frequently contains tubercle bacilli and 

 in such large numbers as even to surprise the research 

 workers in laboratories who busy themselves with these 

 questions. 



Tonney examined the market milk of Chicago in 1910 

 for the presence of tubercle bacilli. In 10.5 per cent of 144 

 samples of raw milk he found tubercle bacilli in sufficient 

 numbers to infect guinea-pigs. Of 19 samples of pasteur- 

 ized milk examined, none contained tubercle bacilli. 



Hess in 1909 examined 107 samples of market milk in 

 New York City, with the result that 17 of them, or 16 per 

 cent, were found to contain tubercle bacilli. 



Anderson examined 233 samples taken in the city of 

 Washington and reported 16, or 6.72 per cent, as positive. 

 The tests made by the Bureau of Animal Industry of the 

 milk in Washington disclosed 7.7 per cent infected. Goler 

 reports about 5 per cent of the milk supply of Rochester, 

 New York, infected. 



To sum up, we have evidence from four typical American 

 cities. A total of 551 samples of milk have been examined 

 in which tubercle bacilli were found in 46, making a percent- 

 age of 8.3. This may be taken as the average percentage 

 for the entire country. As a matter of fact the incidence 



