136 DIPHTHERIA AND PSEUDODIPHTHERIA. 



Put a cover-glass prepared in the usual way for two or three 

 seconds into No. 1 ; then pass into No. 2 and let it remain 

 there for three to five seconds ; wash, air-dry, mount in 

 balsam. The body of the bacteria will be stained brown, 

 and the usually darkly stained granules with the Loeffler 

 method will be stained blue. If the bacilli under examina- 

 tion are true diphtheria bacilli, the majority of them will show 

 the blue granule. If the bacilli are pseudodiphtheritic bacilli, 

 scarcely any or few will show a blue stain in their interior. 



Biologic Characters. The Bacillus diphtherias is aerobic, 

 but can grow in the presence of oxygen, and is therefore a 

 facultative anaerobic ; it is non-motile, has no flagella, does 

 not form spores, and does not liquefy gelatin. 



Its thermal death-point is 58 C. It grows at ordinary 

 room temperature, but slowly. Its maximum of growth is 

 between 37 and 38 C. It is easily killed by disinfectants. 

 Exposure to direct sunlight destroys the bacilli in a few 

 days. In albuminous fluid and in the dark it may live, even 

 when dried, for months. It grows on all artificial culture- 

 media, but best in blood-serum prepared after the formula of 

 Loeffler, a modification of which, employed in many munic- 

 ipal laboratories, is as follows : 



Blood-serum from sheep or calves, 3 parts ; 

 Peptone-bouillon containing 1 per cent. 



of glucose, 1 part. 



Mix, distribute among test-tubes, sterilize, and harden by ex- 

 posing in a slanting position in a steam sterilizer at 97 C. 

 for tw r o hours. 



On this mixture at 37 C. after twelve hours the colonies 

 are round, grayish-white, about the size of a pin-head ; 

 later they become larger, elevated, and yellowish, with the 

 centre more opaque than the periphery. At the end of a 

 few days the colonies have a diameter of from 3 to 5 milli- 

 meters. 



In bouillon at 37 C. the cultures present small clots 

 deposited on the side and at the bottom of the tube. Some 



