THE COLON BACILLUS 383 



and in gelatin shake cultures (Fig. 42), provided the latter 

 medium be made with meat ; " lemco " gelatin, however, 

 generally fails to give gas. On acid potato it forms a 

 straw-yellow or brownish-yellow, moist, thick growth, but 

 if the potato is not fresh and acid in reaction the growth 

 may be colourless. Milk is a good culture medium, and 

 is curdled in twenty- four to seventy- two hours. This 



FIG. 42. Colon bacillus. Gelatin shake culture showing gas 

 production. 



curdling is principally due, not to an enzyme, but to the 

 formation of a considerable amount of lactic acid, though 

 a milk-curdling enzyme has been described by Savage 1 

 as being formed under certain conditions. The gas which 

 is produced in culture media under anaerobic conditions 

 consists of hydrogen and carbon dioxide. Under aerobic 

 conditions marsh gas is stated to be also formed. The 

 ratio of H to C0 2 is about 2 : 1 for dextrose and lactose. 

 In broth it produces a general turbidity without film 

 formation, and the culture gives the indole reaction on 



1 Journ. Pathol. and Bact., November 1904. 



