DIAGNOSIS OF MYCOBACT. TUBERCULOSIS, 437 



2. For the differentiation of T. B. from lepra and 

 smegma bacilli the present methods scarcely suffice. T. B. 

 are difficult to cultivate; lepra and smegma organisms are 

 only very rarely cultivated successfully. For the tincto- 

 rial differences, see pages 422 and 425. 



3. There is no difficulty in differentiating the T. B. 

 from " pseudotubercle bacilli " which grow well at room 

 temperature, so long as only one variety is present. Agar 

 or gelatin plates are prepared and kept at 22. True 

 tubercle bacilli do not grow at all, at least when they come 

 from warm-blooded animals, while the false varieties grow 

 out well in two to four days. Reinoculations are made 

 upon glycerin-agar and into bouillon in order to differen- 

 tiate Myc. phlei and Myc. lacticola. 



We are unable to suggest a method for recognizing cul- 

 turally the true T. B. when associated with large numbers 

 of bacilli resembling it ; in cultures the true T. B. would 

 be overgrown. According to the present state of our 

 knowledge, a guinea-pig must be injected intraperitone- 

 ally with a moderate amount of the mixture. 



If the guinea-pig dies after the intraperitoneal injection 

 of small amounts of culture (one loopful) and without the 

 addition of butter, with well-marked tuberculous changes 

 in the abdominal cavity (enlargement of liver and spleen), 

 and with involvement of the respiratory organs, these speak 

 in favor of true tuberculosis. The histologic examination 

 must give a predominance of true, giant-celled tubercles ; 

 and from the nodes and nodules organisms must be culti- 

 vated which will not grow at room temperature and on ordi- 

 nary nutrient media, but at incubator temperature and upon 

 ascites-glycerin-agar in the case of true T. B. Since death 

 from tuberculosis in guinea-pigs usually occurs six weeks 

 after the infection, before that the few germs resembling 

 the T. B. are absorbed and have disappeared. 



4. To determine whether a person or an animal is tuber- 

 culous, the injection of tuberculin is often made use of. 

 Although it does not lack in individual contradictory re- 

 sults, yet there is no doubt that the tuberculin reaction 

 constitutes a very important aid. 



It is customary to inject cows subcutaneously with 0.3 

 to 0.5 c.c. of tuberculin, and to observe whether an eleva- 



