124 ESSENTIALS OF BACTERIOLOGY 



liquefy gelatin. They are not very resistant, being destroyed 

 by a temperature of 50 C., but they have lived on blood-serum 

 five months. Acid is produced in sugar media. 



Growth. Grow readily on all media, but best on blood-serum 

 mixtures, between temperatures of 20 and 40 C. They are 

 facultative anaerobic; they grow quite rapidly and profusely. 

 Egg cultures (Hueppe's method) give good growths. Passing 

 currents of air increase the growth. 





Fig. 62. Diphtheria bacilli from a culture on blood-serum, stained by 

 Loffler's methylene-blue solution, showing deeply stained points; (x 2000) 

 (Wright and Brown). 



Colonies on Gelatin Plates. At 24 C. little round colonies, 

 white under low power, granular center; irregular borders. 



Stab-cultures. Small, white drops along the needle-track. In 

 glycerin-agar a somewhat profuse growth. 



Potato. On alkaline surface, a grayish layer in forty-eight 

 hours. 



Blood-serum (After Lbffler) . Blood-serum 3 parts, and bouil- 

 lon i part; the bouillon contains peptone, i per cent., sodium 

 chlorid, \ per cent., and dextrin (or glucose), i per cent. 



In a few hours (eight to sixteen) on the white opaque surface 

 a slight moisture is noticeable which, if examined, is composed 



