166 PATHOGENIC BACTERIA 



when cultivated in the laboratory. It possesses the 

 power of coagulating milk and of acid fermentation, 

 with the production of gas, in most of the carbohydrates 

 (sugars and starches) used for the differentiation of 

 bacteria. It does not produce ferments capable of 

 liquefying gelatin or the milk curd. It does, however, 

 break up simpler substances and forms indol, a putre- 

 factive product. 



FIG. 47 



Colon bacilli. Twenty-four-hour agar culture. X 1100 diameters. (Park.) 



The colon bacillus is killed at 60 C. or 140 F. in 

 ten minutes. It resists freezing for a long time, perhaps 

 several months. Drying usually kills in one day, but 

 certain individuals may remain viable for many days 

 or weeks. It is killed by carbolic acid, 1 to 1000, 

 in twenty minutes, or 5 per cent, in two minutes in 

 watery suspension. About the same time hold for 

 bichloride of mercury, 1 to 4000 and 1 to 1000. To 

 weak acids it is resistant, as is shown by its passage 



