SURVIVAL OF PATHOGENS IN SOIL AND WATER 33 



Mycobacterium tuberculosis 



The fate outside the hosts of the bacteria causing tuberculosis in man 

 and in animals has also been studied extensively. Considerable diffi- 

 culty has often been encountered, however, in demonstrating the pres- 

 ence of this pathogen, which must be detected usually by guinea pig 

 inoculation methods. The organism was found to be alive in a dark 

 room after 157 to 170 days, but not after 172 to 188 daysj in diffused 

 light, the longevity was only 124 days. In the incubator, the organism 

 retained its virulence for 2>'i days, but not for 100 days j on ice, virulence 

 was still evident after 102 days but not after 153 days (657). 



Pure cultures of the bovine organism mixed with cow manure and ex- 

 posed in a 2-inch layer in a pasture remained virulent for 2 months in 

 sunlight and longer in the shade. Tubercle bacteria were still alive in a 

 garden soil on the 213th day and dead on the 230th day. They were 

 alive in buried tuberculous guinea pigs on the 71st day, and dead on 

 the 99th day. In running water, they survived for more than a year 

 (86). Mycobacterium tuberculosis survived for 309 days in sputum 

 kept in darkness, even when completely desiccated j in decomposing 

 sputum, living organisms could be isolated after 20 days but not after 

 25 days (871a). Under conditions prevailing in southern England, it 

 was found ( 1020) that the tubercle organism may remain alive and viru- 

 lent in cow's feces exposed on pasture land for at least 5 months dur- 

 ing winter, 2 months during spring, and 4 months during autumn j in 

 summer, no living organisms were demonstrated even after 2 months. 

 Under protection from direct sunlight, the survival period was longer. 

 Feces protected from earthworms yielded viable cells even after 5 

 months. Virulent bacteria were still present in stored liquid manure at 

 least 4 months after infection, though during this time a gradual reduc- 

 tion in virulence of the organism was observed. 



The addition of manure to soil was found to favor the survival of the 

 tubercle bacteria, as indicated by a higher proportion of test animals 

 becoming tuberculous when the amount of manure added to the soil was 

 increased (613). Positive tests were obtained for soil and manure after 

 178 days but not later. The organism survived on grass for at least 49 

 days. Rhines (780) found that M. tuberculosis multiplied in sterile soil 



