200 



BACTERIA 



FIG. 60. B, 

 sulatus, agar 

 gas formation. 



aerogenes cap- 

 culture showing 

 (Williams.) 



by all the basic dyes, and holds the 

 stain in Gram's method. Staining 

 shows that it possesses a capsule. 



Habitat. The soil, the intestines, 

 and, sometimes, the skin of man. 



Vital Characteristics. Vital re- 

 sistance is low, the thermal death- 

 point being 58C. with ten minutes' 

 exposure, while spores require ten 

 minutes' boiling for killing. It 

 grows best at body temperature. 

 Has lived for one hundred days on 

 culture media in the incubator. It 

 is an anaerobe. 



Chemical Activities. Produces 

 gas; does not usually liquefy gela- 

 tine, but curdles milk (Fig. 60). 



Cultures. Grows best in neutral 

 or alkaline media, producing abund- 

 ant gas. Colonies appear grayish 

 or brownish-white, and are often 

 surrounded by projections which 

 are feathery or hair-like. On agar 

 strict anaerobic conditions are 

 necessary for growth, gas bubbles 

 appear in the media, and the agar 

 may be forced out of the tube in 

 stab cultures. In bouillon it grows 

 under anaerobic conditions. The 

 growth is rapid, bouillon is clouded, 

 and a froth appears on the surface. 

 After a few days the medium be- 

 comes clear, owing to the sedi- 

 mentation of the bacilli. Growth 



