118 BACTERIOLOGY FOR NURSES 



Many special methods of staining the organism 

 are used. The diphtheria bacillus grows best upon 

 a slightly alkaline medium at body heat, 37° C. (98.6° 

 F.), often showing minute colonies within twelve or 

 fifteen hours, which are of a grayish white color with 

 granular surfaces and fringed edges. 



Resistance. — The resistance of the diphtheria 

 bacillus constitutes one of its chief dangers as an 

 infective agent. Growths upon ordinary media 

 retain their vitality from six weeks to twelve or fifteen 

 months, and observers have isolated Uving bacilU 

 from dried diphtheritic membrane after a lapse of 

 eight months. It is said that bacilli in dry membrane 

 will resist dry heat at 98° C. (208.4° F.) for an hour, 

 but will be killed by moist heat at 55° C. (131° F.) 

 in forty-five minutes. 



This extreme resistance probably explains many 

 instances of outbreaks of diphtheria of unknown 

 origin, as the bacilli could easily be carried in the 

 dry state for long distances by means of clothing 

 and many other articles. 



Diphtheria Infection in Man. — The mucous mem- 

 branes of the human body are the favorite site for 

 the development of the bacilli of diphtheria. The 

 pharynx is most commonly infected, but the larynx 

 or nasal membranes are quite often the site of infec- 



