486 



PATHOGENIC MICROORGANISMS 



Biological Considerations. The tubercle bacillus is dependent upon 

 the access of oxygen. Its optimum temperature is 37.5 C. Tem- 

 peratures below 30 and above 42 C. inhibit its growth. In fluid media, 

 the bacilli are killed by 60 in fifteen to twenty minutes, by 80 in five 



minutes, by 90 in one to two min- 

 utes. They will withstand dry heat 

 at 100 C. for one hour. They are 

 resistant to cold. The comparatively 

 high powers of resistance of the bacil- 

 lus are attributed to the protective 

 qualities of the waxy cell membrane. 1 

 The life of cultures, kept in favor- 

 able environment, is from two to eight 

 months, varying to some extent with 

 the nature of the culture medium. 

 The viability of the bacilli in sputum 

 is of great hygienic importance. In 

 most sputum they may remain alive 

 and virulent for as long as six weeks, 

 in dried sputum for more than two 

 months. 2 



Five per cent carbolic acid kills 

 the bacilli in a few minutes. 3 Used 

 for sputum disinfection, where the 

 bacilli are protected, complete disin- 

 fection requires five to six hours. Bi- 

 chloride of mercury is not very efficient 

 for sputum because of the formation 

 of albuminate of mercury. For room 

 is efficient. Direct sunlight kills in 



FIG. 104. CULTURE OF BACILLUS 

 TUBERCULOSIS IN FLASK OF GLYC- 

 ERIN BOUILLON. 



disinfection, formaldehyde gas 

 a few hours. 



Pathogenicity. The tubercle bacillus gives rise in man and suscep- 

 tible animals to specific inflammation which is so characteristic that a 

 diagnosis of tuberculosis may be made by histological examination, 

 even without the finding of tubercle bacilli. The foci known 

 as tubercles have been studied by Baumgarten 4 and many others 



1 Th. Smith, Jour. Exper. Med., 1899; Grancher et Ledoux-Lebard, Arch, de med. 

 exper;, 1892; Galtier, Compt. rend, de 1'acad. des sci., 1887. 

 *Schell und Fischer, Mitt. a.'d. kais. Gesundheitsamt, 1884. 

 3 De Toma, Ann. di med., 1886. . 4 Baumgarten, Berl. klin. Woch., 1901. 



