Cultivation 



711 



They usually develop more rapidly upon fluid than solid media. 

 The organism is purely aerobic, and the surface growth formed 

 upon liquids closely resembles that upon solids. 



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 



Fig. 282. — Bacillus tuberculosis; adhesion cover-glass preparation from a four- 

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



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. 

 The human bacillus has been shown by Theobald Smith* to produce 

 acid, the bovine bacillus to produce alkali in artificial cultures. . 



Relation to Oxygen. — The tubercle bacillus is a strict aerobe and 

 grows only upon the surface of the culture-media. 



Temperature Sensitivity. — The bacillus is sensitive to tempera- 

 ture variations, not growing below 29°C. or above 42°C. Rosenauf 

 found that an exposure to 6o°C. for twenty minutes destroyed the 

 infectiousness of the tubercle bacillus for guinea-pigs. 



Effect of Light. — ^It does not develop well in the hght, and when 

 its virulence is to be maintained should always be kept in the dark. 



* "Jour. Med. Research," 1905, xin, 253, 405. 



t "Hygienic Laboratory," Bulletin No. 24, Jan., 1908. 



