6i8 Bacillus Coli 



where the moisture of condensation allows it to spread out at the 

 bottom. Kruse says that crystals may form in old cultures. 



Bouillon. — Bouillon is densely clouded by the growth of the bac- 

 teria, a delicate pellicle at times forming upon the surface. There is 

 usually considerable sediment in the culture. 



Potato. — Upon potato the growth is luxuriant. The bacillus 

 forms a yellowish-brown, glistening layer spreading from the line 

 of inoculation over about one-half to two-thirds of the potato. 

 The color varies considerably, sometimes being pale, sometimes quite 

 brown, sometimes greenish. It cannot, therefore, be taken as a char- 

 acteristic of much importance. The growth on potato may be almost 

 invisible. 



Milk. — In milk rapid coagulation and acidulation occur, with the 

 evolution of gas. The culture gives off a fecal odor. Litmus added 

 to the culture-media is first reddened, then decolorized by the bacilli. 



Vital Resistance. — It is quite resistant to antiseptics and germi- 

 cides, and grows in culture-media containing from 0.1-0.2 per cent, 

 of carbolic acid. It is, however, easily killed by heat, and is 

 destroyed by exposure to 6o°C. for ten minutes. 



Metabolic Products. — Wiirtz found that Bacillus coli produced 

 ammonia in culture-media free from sugar, and thus caused an in- 

 tense alkaline reaction in the culture-media. The cultures usually 

 give off an odor that varies somewhat, but is, as a rule, unpleasant. 



Nitrates are reduced to nitrites by the growth of the bacillus. 



In bouillon containing i per cent, of dextrose, lactose, levulose, 



galactose, and mannite, the colon bacillus splits up the sugar, lib- 



H 2 

 crating CO2 and H, the gas formula being p7^ = 7- This gas 



formula is very constant for the micro-organisms of the colon group 



and forms one of their most important differential characteristics. 



In calculating the gas formula Winslow has shown that some care 



ought to be taken to do it at the appropriate time. According to his 



H 2 

 observations the 7;^^- • - formula only obtains between the twenty- 



fourth and forty-eighth hours. Before this period the H, which is 

 first formed, preponderates; after it the CO2 may preponderate. 

 In sugar-containing bouillon, acetic, lactic, and formic acids are 

 produced. It does not ferment saccharose. When a similar bacillus 

 is found to ferment saccharose it is best regarded as a subspecies 

 or separate type, for which Dunham has introduced the name 

 Bacillus coli communior. 



The bacillus requires very little nutriment. It grows in Uschin- 

 sky's asparagin solution, and is frequently found living in river and 

 well waters. 



Indol is formed in both bouillon and peptone solutions, but phenol 

 is not produced. The presence of indol is best determined by Sal- 

 kowski's method {q.v.}. 



