88 BACTERIOLOGY FOR NURSES 



a more scanty growth than sub-cultures, but are 

 always distinctly characteristic, appearing as dry 

 masses like dry meal spread over the medium and of 

 dull whitish or pale drab color, sometimes emitting a 

 peculiar odor. Growth occurs within a narrow range 

 of temperature, 37-38 C. (98.6 F.-100.4 F.), which 

 corresponds to the normal temperature of the human 

 body ; but by a series of sub-cultures, growths have 

 been observed in a temperature as low as 23 C. (73.4 

 F.) . The tubercle bacillus is one of the few organisms 

 which grow better upon a slightly acid medium. 



Powers of Resistance. - - The resistance of the 

 tubercle bacillus is considerable, as it retains its 

 vitality outside of the human body for some time, 

 which constitutes the chief danger in the transmission 

 of the disease. The bacilli in dried sputum will re- 

 tain their vitality while floating in the air for several 

 days, and if lodged in a cool dark place, may survive 

 for six months. They are highly resistant to dry 

 heat, surviving 100 C. (212 F.) for more than an 

 hour, but will be killed by moist heat at 60 C. 

 (140 F.) in twenty minutes. Freezing does not 

 always destroy them, but exposure to sunlight will 

 kill them in a few hours. 



Of all of the chemicals used for germicidal purposes 

 carbolic acid and its preparations have been found 



