PATHOGENIC BACTERIA IN MILK 219 



which any douht exists, it can be cleared up by cultivations 

 from the glands, etc., of the inoculated animal. This difficulty 

 cannot arise in connection with ordinary milk examinations, 

 but has to be remembered and guarded against in experiments 

 directed to determine the thermal death-point of the tubercle 

 bacillus in milk or other substance. 



The possible presence of acid-fast bacilli in milk other 

 than the tubercle bacillus, while it diminishes the value of 

 simple microscopic examination, does not to any appreciable 

 extent interfere with the inoculation test. The death of the 

 guinea-pig, with lesions apparently those of tuberculosis, 

 is almost certainly due to tubercle bacilli. As a routine 

 procedure, and certainly in any cases of doubt, cultures should 

 be made on glycerine agar from the enlarged glands. The 

 simulating acid-fast bacilli grow readily and rapidly upon this 

 and other nutrient media, unlike the tubercle bacillus. 



The American Committee on standard milk methods ^ 

 give a further test. They remark : 



Tuberculous guinea-pigs may be differentiated from non-tuber- 

 culous by giving suflBcient crude tuberculin (2 c.c.) subcutaneously 

 to cause the death of the tuberculous animals in 24 hours. Of 

 about 250 guinea-pigs tested in this way no animal that did not 

 have tuberculosis died. Two or three that had slight lesions did 

 not die but became sick. It was noted that all the animals died 

 whose lesions had become caseated. 



The reaction seems of distinct service in eliminating infections 

 with acid-fast organisms, and the suggestion is made that with some 

 modification the procedure may have a distinct place as an aid in 

 differentiating true tuberculosis from infections with other acid-fast 

 organisms which produce tubercular-like lesions. 



The Differentiation of Human and Bovine Tubercle 



Bacilli 



As pointed out in Chapter VII. two distinct types (apart 

 from the avian type) of tubercle bacilli are met with, accord- 

 ing as the bacilli are of bovine or human type, generally 

 corresponding to their being of bovine or human origin 

 respectively. The differences are relative rather than absolute 

 and to some extent intermediate forms are met with. They 



^ American Journ. of Puhlic Health, 1910, xx. p. 338. 



