BACILLUS DIPHTHERIA 565 



easily killed by chemical disinfectants in the strengths customarily 

 employed. H2O2 seems especially efficacious in killing the organisms 

 rapidly. 



Cultivation. The diphtheria bacillus grows readily on most of 



the richer laboratory media. It will grow upon media made of meat 

 extract, but develops more luxuriantly on all those which have a meat 

 infusion as their basis. While it will grow upon both acid and alkalin 

 media, it is sensitive to the extremes of both, the most favorable reaction 

 for its development being probably about 0.5 per cent alkalinity ex- 

 pressed in terms of N/l NaOH. Animal proteins added to the media, in 

 the form of blood serum, ascitic fluid, or even whole blood, increase 

 greatly the rapidity and richness of its growth. Horse serum is supposed 

 by some to be especially favorable. 10 



Loeffler's Medium. The most widely used medium for the cultiva- 

 tion of this bacillus is the one devised by Loeffler. This consists of; 



Beef blood serum 3 parts 



One per cent glucose meat-infusion bouillon 1 part 



The mixture is coagulated at 70 a C. in slanted tubes and sterilized at 

 low temperatures by the fractional method. Upon this medium 'the 

 diphtheria bacillus in twelve to twenty-four hours develops minute, 

 grayish-white, glistening colonies. These enlarge rapidly, soon out- 

 stripping the usually accompanying streptococci. The medium seems 

 to possess almost selective powers for the bacillus and, for this reason, 

 it is especially valuable for diagnostic purposes. 



Meat-infusion Agar. Upon slightly alkalin meat-infusion agar the 

 bacillus develops readily, though less so than on Loeffler 's serum. 

 Organisms which have been on artificial media for one or more genera- 

 tions may grow with speed and luxuriance upon this medium. When 

 planted directly from the human or animal body upon agar, however, 

 growth may occasionally be slow and extremely delicate. Colonies on 

 agar appear within twenty-four to thirty-six hours as small, rather 

 translucent, grayish specks. The appearance of these colonies is quite 

 characteristic and easily recognized by the practiced observer. Surface 

 colonies are irregularly round or oval, showing a dark, heaped-up, 

 nucleus-like center, fringed about by a loose, coarsely granular disk. 

 The edges have a peculiarly irregular, torn appearance which distin- 

 guishes them readily from the sharply defined streptococcus colonies. 



10 Michel, Cent. f. Bakt., 1897. 



