668 Tuberculosis 



Appearance of the Cultures. Irrespective of the media upon 

 which they are grown, cultures of the tubercle bacillus present certain 

 characteristics which serve to separate them from the majority of 

 other organisms, though insufficient to enable one to identify them 

 with certainty. 



The bacterial masses make their appearance very slowly. As a 

 rule very little growth can be observed at the end of a week, and 

 sometimes a month must elapse before the growth is distinct. 



They usually develop more rapidly upon fluid than upon solid 

 media. The organism is purely aerobic, and the surface growth 

 formed upon liquids closely resembles that upon solids. 



Fig. 275. Bacillus tuberculosis; adhesion cover-glass preparation from a four- 

 teen-day-old blood-serum culture. X 100 (Frankel and Pfeiffer.) 



It is dry and lusterless, coarsely granular, wrinkled, slightly 

 yellowish, and does not penetrate into the substance of the culture- 

 medium. It sometimes extends over the surface of the medium and 

 spreads out upon the contiguous surface of moist glass. 



When the medium is moist, the bacterial mass may in rare in- 

 stances be shining in spots. When the medium is dry, it is apt to 

 be scaly and almost chalky in appearance. 



The organism grows well when once successfully isolated, and, 

 when once accustomed to artificial media, not only lives long (six 

 to nine months) without transplantation, but may be transplanted 

 indefinitely. 



Reaction. The tubercle bacillus will grow upon otherwise ap- 

 propriate media whether the reaction be feebly acid or feebly 

 alkaline. 



Relation to Oxygen. The tubercle bacillus requires oxygen, and 

 grows only upon the surface of the culture-media. 



