284 ORGANISMS RESEMBLING BACILLUS TYPHOSUS 



liquefaction of the gelatin. On agar-agar and blood-serum 

 a heavy, grayish-white, moist, translucent film develops along 

 the track of the needle. Bouillon is clouded, but as the 

 growth settles to the bottom of the tube the bouillon becomes 

 clear. A surface membrane is formed at times. 



In media containing peptone indol is formed. Its growth 

 in media containing sugar is accompanied by the evolution of 

 much gas, sufficient to break the medium into chunks. The 

 fermentation-tube can be used to demonstrate gas-production. 



FIG. 129. 



Colon bacilli : twenty-four-hour agar culture. X 1100. (Park.) 



Milk is rapidly coagulated. Litmus solution is decolorized by 

 the production of large quantities of acid. 



On potato the growth is quite characteristic. It is very 

 luxuriant, forming a thick moist brown layer which spreads 

 rapidly over the entire surface of the potato. At times the 

 rest of the potato is discolored, turning distinctly green. 



The colon bacillus is very resistant to acids and antisep- 

 tics. An exposure of ten minutes to a temperature of 60 C. 

 is fatal. 



Pathogenesis : Although Bacillus coli communis is ordinarily 

 non-pathogenic for man, it is not infrequently found in 



