264 



VETERINARY BACTERIOLOGY 



plates the colonies are moist, grayish white, opaque, becoming 

 darker and more coarsely granular. Gelatin is not liquefied. 

 Stab cultures in gelatin show a filiform growth along the line of 

 puncture, and a spreading growth at the surface. The agar cul- 

 tures resemble those on gelatin. Bouillon is quickly clouded, 

 sometimes with formation of a pellicle. On potato a moist, 

 spreading growth occurs, and the potato is darkened. Milk is 



coagulated by the forma- 

 tion of acids; the curd 

 shrinks, but is -not 

 digested. 



Physiology. B. coli 

 is aerobic and facultative 

 anaerobic. Its optimum 

 growth temperature is 

 37, but growth is 

 luxuriant at room-tem- 

 perature and even below. 

 The thermal death-point 

 is 60 for fifteen min- 

 utes. Many carbohy- 

 drates are fermented, 

 with production of acid 

 and gas. Among these 



are dextrose, lactose, and maltose, and, in about half the 

 strains isolated, saccharose. The gas formula from dextrose is 



H 2 



approximately ^- > < j. Indol is produced in Dunham's solu- 

 tion. Peptonizing and proteolytic enzymes have not been demon- 

 strated. 



Pathogenesis. The following quotation from Jordan epitom- 

 izes our present estimate of the pathogenicity of B. coli: " The 

 common occurrence of agonal or postmortem invasion of the body 

 by the colon bacillus tends to diminish the value of the supposed 

 evidence derived from finding the colon bacillus in the internal 

 organs after death, and there can be no doubt that the role in 

 human pathology assigned to the colon bacillus by some inves- 

 tigators, notably certain French bacteriologists, has been greatly 



Fig. 109. Bacillus coli showing the flagella 

 (Migula). 



