104 MEDICAL BACTERIOLOGY 



Plain Agar. In 18 to 24 hours, small, round, moist, whitish-gray colonies 

 appear; these coalesce forming a thin grayish opaque film. 



Glycerin Agar. On glycerin agar the growth has the same appearance, but 

 is slightly more abundant. 



Loeffler's Blood Serum. On Loeffler's blood serum growth is the same as on 

 agar. 



Gelatin. Surface cultures are the same as on agar. Gelatin stab cultures 

 show a continuous yellowish-white growth along the entire length of the stab and 

 on the surface. 



Gelatin is not liquefied. 



Potato. On the surface of potato slants a moist, yellowish film appears in 24 

 to 48 hours; as it ages it becomes thicker and darker, eventually brown. 



Milk is acidulated and coagulated in from 12 to 48 hours. 



The colon bacillus produces indol. It does not form spores. 



The colon bacillus ferments glucose, lactose, saccharose, maltose and levu- 

 lose, with both gas and acid production. 



Resistance. The colon bacillus is not destroyed by freezing, boiling kills it 

 instantly, moist heat at 6oC. kills it in half an hour. It is destroyed in the hot- 

 air sterilizer in less than an hour at iooC. Dry, it survives for half a year or 

 more. Exposure to direct sun rays kills the colon bacillus in from 4 to 30 hours. 

 In feces, soil and water, under favorable conditions, colon bacilli remain alive for 

 many months. Resistance to chemical germicides is not great; a 2 per cent, 

 phenol solution will kill the colon bacillus in several minutes. 



Toxin. The colon bacillus produces an intracellular toxin. Filtrates from 

 sterilized heated cultures, injected into animals give rise to the same toxic 

 symptoms and signs as infection with living bacilli. 



Agglutinins occur in the blood of infected persons and in the blood of animals 

 immunized against the colon bacillus. These agglutinins are not only specific 

 for the colon bacillus, but show an especially strong action on the particular 

 strain of the organism responsible for their production. 



Lysins and Precipitins also occur in the blood of animals immunized against 

 the colon bacillus. 



Pathogenesis. The fact that colon bacilli in enormous numbers are con- 

 stant inhabitants of the intestinal canal would seem to indicate a lack of patho- 

 genic power of the bacillus or a gradual acquirement of immunity on the part of 

 the host. There are marked variations in virulence, some strains of colon 

 bacilli being sufficiently virulent to cause septicemia and death. As a rule, they 

 are but slightly pathogenic. 



In health these organisms are confined to the intestinal canal, but when dis- 

 ease or injury reduces the vitality of the intestinal wall, peritoneum, or any organ 

 adjacent to the intestines, colon bacilli are prone to migrate and attack the im- 

 paired organ; thus, they are often found infecting an appendix, gall-bladder, peri- 

 toneum, fallopian tube or urinary bladder. 



Through causes, and by no means not well understood, colon bacilli migrate 

 to and are often the cause of renal infections, acute, chronic or suppurative. 



