322 THE TUBERCLE BACILLUS 



and glycerin-potato the avian bacillus frequently forms a wrinkled or warty 

 growth resembling a culture of human tubercle bacilli ; but the characteristic 

 difference is evident when the growth is touched with the spatula."] 



SECTION III. BIOLOGICAL PROPERTIES. 

 1. Viability and virulence. 



In determining the viability of the tubercle bacillus, animal inoculation, 

 not artificial cultivation, must be the test [because sub-cultures often fail 

 though the culture used for sowing them may be alive especially if the 

 operator has not had considerable experience in dealing with cultures of the 

 tubercle bacillus]. 



In cultures, the tubercle bacillus is only slightly resistant to adverse con- 

 ditions and this is one of the arguments in favour of the view that it does 

 not form spores. Exposure to 70 or 75 C. for 10 minutes kills cultures of 

 the bacillus in liquid media. 



[F. Griffith (for the English Commission) made numerous tests on bacilli 

 grown on various media and concludes that " cultures " (of mammalian or 

 avian tubercle bacilli) " will maintain their vitality for long periods whether 

 kept in the incubator or at room temperature." Avian bacilli in one culture- 

 tube were found alive after 1067 days, and bovine bacilli similarly after 

 990 days : " but no distinction could be drawn between the types of bacilli 

 tested."] 



Agar cultures [are said to] lose their virulence after a few months [but 

 F. Griffith found that " little if any attenuation " (of the bovine bacillus) 

 " was caused by residence on artificial media " (serum and glycerin-serum) 

 for periods up to 1487 days. Human tubercle bacilli tested after from 2-3 

 years' artificial cultivation (on serum) showed no appreciable diminution in 

 virulence (A. S. Griffith).] 



[Calmette and Guerin state that cultures on glycerin-bile-potato (p. 318) 

 are at first increased in virulence but that repeated sub -cultivation on that 

 medium diminishes the virulence of the bacilli for certain animal species.] 



In moist sputum the bacillus is not destroyed at 75 C. but is killed in 

 5 minutes at a temperature of 100 C. 



Cultures of the tubercle bacillus, or tubercle bacilli in sputum, retain their 

 vitality for a long period when dried at the ordinary temperature of the air. 

 Under these conditions, the bacilli may retain their virulence for several 

 months (Galtier) ; they are not destroyed by exposure to a dry temperature 

 of 100 C. for 2 or 3 hours and are capable of resisting a temperature of 70 C. 

 for more than 7 hours (Welch, Grancher, Ledoux-Lebard), 



The combined action of desiccation and sunlight [is said to], attenuate the 

 virulence of the bacillus (Candler, Koch, Migneco and Kansome). 



Zilgen mixed some dust with dried tuberculous sputum and exposed the 

 mixture to the action of sunlight : under these conditions, the tubercle 

 bacillus retained its virulence for about 140 days. According to de Thoma 

 the virulence of the bacilli in sputum left in the patient's room disappears 

 after two months and a half but is retained indefinitely when the sputum is 

 kept in the dark under the same conditions. 



The virulence of tubercle bacilli in sputum exposed to the alternate action 

 of moisture and desiccation is retained for several months (Malassez and 

 Vignal). 



The tubercle bacillus appears to maintain its vitality in water for a long 

 time : it has been recovered from sterile water after 70 days (Chantemesse 



