Ill THE BACTERIA FOUND IN MILK 43 



Group 5. — Acid-fast Bacilli 



Within the last two decades the number of bacilli known 

 to be resistant to decolorisation by acid after staining has 

 greatly increased, and such acid - fast bacilli, as they are 

 conveniently called, have been shown to be widely distributed 

 in nature. They have been obtained from the human body 

 (mouth, smegma, etc.), and outside the body from manure, 

 milk, butter, various grasses, etc. 



Of no particular significance in themselves they owe their 

 importance to the fact that they superficially resemble the 

 tubercle bacillus in being acid-fast, in their morphology and 

 less characteristically in their pathological effects upon rodents. 

 Their possible presence has always to be kept in mind in con- 

 nection with the diagnosis of tubercle bacilli in milk. 



From the point of view of milk and tuberculosis the 

 varieties of greatest interest are the butter bacillus of Eabino- 

 witch and Petri, Moeller's timothy -grass bacilli, I. and II., 

 Johne's bacillus, and the mist bacillus. The smegma bacilli 

 are also important members of this group. Cowie showed 

 that acid -fast bacilli are to be found around the external 

 genitals, etc., of some of the lower animals. It is not clear if 

 these bacilli are identical with the human smegma bacilli. 



The Butter Bacillus. — This bacillus serves as a good illus- 

 tration of the group. It was isolated independently by Eabino- 

 witch and Petri from butter. Morphologically it is shorter 

 and thicker than the tubercle bacillus, but superficially re- 

 sembles it. Long unbranched thread-like forms are sometimes 

 met with. Culturally it grows rapidly upon agar and glycer- 

 ine agar, a well-marked thick crinkled growth being present 

 after 3 to 4 days. It grows equally quickly in glycerine 

 broth, a crinkled scum being present after 2 to 3 days' 

 growth, the broth having an unpleasant odour. It will grow 

 in or on these media at room temperatures. Injected intra- 

 peritoneally, mixed with butter, into guinea-pigs, it produces 

 lesions which closely resemble those produced by the tubercle 

 bacillus, frequently causing the death of the animal. 



The other acid -fast bacilli are very similar. They all 

 agree with the tubercle bacillus in their resistance to de- 

 colorisation by acid after staining, while morphologically they 



