DIPHTHERIA BACILLUS. 337 



But though the morphology of the diphtheria bacillus 

 is more regular under some circumstances than others, 

 its chief morphological characteristic is its irregularity 

 of form and size. 



Biology. The Klebs-Loffler bacillus is non-motile 

 and non-liquefying. It is aerobic. It grows most 

 readily in the presence of oxygen, but also without 

 it; it is thus facultative anaerobic. It does not form 

 spores. Its thermal death-point with ten minutes' 

 exposure is about 58 C., and with longer exposure a 

 lower temperature; it is more easily destroyed by dis- 

 infectants than many other bacteria. In the dry state 

 and exposed to diffuse light diphtheria bacilli usually 

 die in a few days or may live for weeks or months; 

 when in the dark, or protected by a film of mucus or 

 albumin, they may live for even longer periods. Thus 

 I found scrapings from a dry bit of membrane to 

 contain vigorous and virulent living bacilli for a 

 period of four months after removal from the throat, 

 and if the membrane had not been at that time com- 

 pletely used, living bacilli could probably have been 

 obtained for a much longer period; in culture media 

 when kept at the blood heat they usually die after a 

 few weeks, but under certain conditions, as when sealed 

 in tubes and protected from heat and light, they retain 

 their virulence for years. The bacillus is not sensitive 

 to cold, for I found it to retain its virulence after ex- 

 posure for two hours to several hundred degrees below 

 zero. It begins to develop, but grows slowly, at a 

 temperature of 20 C., or even less. It grows more 

 rapidly as the temperature rises, and attains its maximum 

 development at 37 C. It may grow at a temperature 

 as high as 41 C. and retain its virulence for months. 



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