112 MILK BACTERIA AND HEALTH. 



percentage of the cases. There is thus a considerable oppor- 

 tunity for the contamination of market milk by tubercle 

 bacilli. 



4. If the tuberculosis infection is located elsewhere in the 

 body, and not in the mammary gland, the contamination of 

 the milk is uncertain. If the infection is a slight one and 

 involves only a few small glands, it is quite certain that the 

 milk will not be infected with the tubercle bacilli. If, how- 

 ever, the infection is a generalized form of tuberculosis, dis- 

 tributed more or less through the body, it is more likely that 

 the milk will be infected. It is not yet positively known 

 whether an animal that has not tubercular infection in 

 the mammary gland, ever produces milk infected with bac- 

 teria, except in cases of generalized tuberculosis. This, how- 

 ever, is a matter of little practical importance, because it is 

 certain that many an animal with no visible infection of the 

 udder may have minute tubercles in the mammary gland so 

 that her milk will be liable to be contaminated with the bacilli, 

 Consequently, many an animal with no external signs of 

 udder tuberculosis may give milk which is infected with the 

 tubercle bacillus. 



5. Abundant evidence demonstrates that market milk fre- 

 quently does contain violent pathogenic tubercle bacilli. 

 These bacteria can be detected by microscopic study of the 

 milk, although this means is very difficult and uncertain. 

 They can also be found by experiments upon animals, for 

 market milk has in many cases been proved to be capable of 

 producing tuberculosis in experimental animals. The per- 

 centage of market milk which contains the tubercle bacillus 

 cannot be stated, since it varies widely with different locali- 

 ties. Similar virulent tubercle bacilli are found in market 

 butter. 



6. It has been demonstrated that not only can the bacillus 

 from mankind produce tuberculosis in animals, but that the 

 bacillus from animals may produce at least a mild form of the. 



