TUBERCULOSIS IN GUINEA PIG. 67 



THE GROUP OF ACID-FAST BRANCHING BACILLI. 



There is a large and ever-increasing number of organisms which 

 have the same staining reactions as the tubercle bacilli, but which 

 differ in four important essentials of 



1. Growing readily on any media. 



2. Showing more or less abundant growth or colonies in 

 twenty-four hours. 



3. Having no pathogenic power for guinea-pigs when inocu- 

 lated subcutaneously. 



4. Not requiring body temperature for development, but 

 growing at room temperature. 



Many of these organisms, if injected intraperitoneally into guinea- 

 pigs, will produce a peritonitis with false membrane. Some also 

 produce granulation tissue nodules which may be confused with true 

 tubercles. For this reason it is well to study the lesions in experi- 

 mental tuberculosis in the guinea-pig. Injected subcutaneously, on 

 either or both sides of the posterior abdomen with the needle pointing 

 toward the inguinal glands, we may have caseation and ulceration at 

 the site of inoculation. The glands in relation enlarge and caseate. 

 Smears from these show T. B. The marked and characteristic change 

 is the enormous enlargement of the spleen, which is studded with 

 grayish and yellow tubercles. Make smears and cultures from the 

 spleen. The death of the guinea-pig usually occurs in about two 

 months. The lesions may be looked for at three to five weeks. 



These nonpathogenic acid-fast bacilli are of greatest importance by 

 reason of their possible confusion with the true tubercle bacilli. 

 Their colonies correspond more or less with different types of tubercle 

 bacilli colonies, being either dry and wrinkled like human or moist and 

 irregularly flat as avian. Eventually the moist colonies become dry 

 and wrinkled. They have been isolated from 



1. Butter and milk. 



2. From grasses, especially in timothy grass infusion. 



3. In various excretions of animals, as in dung, urine, etc. 



4. Normally in man from skin, nasal mucus, cerumen and 

 tonsillar exudate. 



