340 



MANUAL OF BACTERIOLOGY. 



medium the growth consists of small white or cream-colored, 

 slightly elevated colonies, which may become confluent. The 

 morphology of the bacillus is most characteristic when it is culti- 

 vated on blood-serum. It also grows upon glycerin-agar. 

 On potato it grows only if the potato is first treated with soda 

 solution (i per cent.) so as to neutralize the acidity of this 

 medium.* In alkaline bouillon containing dextrose or muscle- 



FIG. 87. Bacillus of diphtheria stained by FIG. 88. Swab and culture- 



Neisser's method. (X 1000.) tube used in the diagnosis of 



diphtheria. 



sugar the reaction becomes acid in forty-eight hours. t The 

 reaction of the bouillon subsequently becomes alkaline. The 

 growth may form a pellicle over the surface of the bouillon. It 

 has also been successfully cultivated on various media to which 

 egg-albumen has been added. 



It is killed by a moist heat at about 60 C. in ten minutes. 

 It is very resistant to drying. 



* Giinther. Loc. cit. 



f Kolle and Wassermann. Loc. cit. p. 769-770. 



