234 



VETERINARY BACTERIOLOGY 



tions glycerin-agar plates may be poured from the growth on 

 blood-serum. It grows well upon most of the laboratory media. 

 Upon Loffler's blood-serum distinct colonies are sometimes visible 

 within twelve hours as minute, pin-point, translucent dots; these 

 enlarge, and within twenty-four hours show as small, opaque, 

 gray colonies, usually discrete. The organism develops somewhat 

 less luxuriantly upon agar and gelatin, although repeated trans- 

 fers tend to increase the luxuriance. Growth occurs in milk, 

 with but little or no observable change in the medium. Broth 

 may be clouded. A delicate film or pellicle forms on the surface 

 after a time, and if transfers of this are made to fresh broth, the 



growth may be largely con- 

 fined to pellicle production. 

 Advantage is taken of this 

 fact in growing the organ- 

 isms in production of diph- 

 theria toxin. 



Physiology. This or- 

 ganism is aerobic. Upon 

 culture-media it will remain 

 alive for long periods. 

 Desiccation of a diphther- 

 itic membrane does not 

 necessarily destroy the 

 bacillus, and it has been 

 isolated from such after a 

 period of months. The 

 heat of pasteurization, 60 



for thirty minutes, destroys it. In the dried condition it is more 

 resistant. Dextrose is fermented by virulent forms in general, 

 with the production of acid, but no gas. Lactose is not fer- 

 mented. The non-virulent types are believed to show less power 

 of acid production. Nitrates are reduced to nitrites. No indol 

 is produced. Proteolytic enzymes are not formed; gelatin is not 

 liquefied. 



Pathogenesis. Mechanism of Disease Production. Diphtheria 

 is one of the best examples of a toxemia, as the organism remains 

 upon the surface of the mucous membranes and in the necrotic 



Fig. 100. Bacillus diphtherias, mount 

 from blood-serum showing the character- 

 istic metachromatic granules (Frankel and 

 Pfeiffer). 



