ISOLATION OF THE COLON BACILLUS. 59 



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ferments saccharose with a gas ratio ^- approaching-, 



and another does not. As a rule, a strong acid reaction 

 is developed in all sugar-containing media. The or- 

 ganism reduces nitrates to nitrites and sometimes to 

 ammonia. It coagulates casein in litmus milk, and 

 reduces the litmus with subsequent slow return of the 

 color (red), and forms indol in peptone solution. Many 

 cultures of this organism are fatal to guinea-pigs when 

 the latter are inoculated subcutaneously with I c.c. of a 

 twenty-four-hour bouillon culture, and most cultures 

 produce death when this amount is inoculated intraperi- 

 toneally. Although not a spore-forming bacillus, and in 

 general not possessing great resistance against anti- 

 septic substances, B. coli seems to be less susceptible to 

 phenol than are many other forms, especially certain 

 water- bacteria. 



The Wurtz litmus-lactose-agar plate (Wurtz, 1892), as 

 noted in Chapter IV, furnishes one ready method for the 

 isolation of B. coli from water, and it was used by Sedg- 

 wick and Mathews for the purpose as early as 1893 

 (Mathews, 1893). The process is based upon the fact 

 already alluded to, that B. coli readily ferments lactose 

 with the formation of acid. If, therefore, plates are made 

 with agar containing both lactose and litmus, the colon 

 colonies develop as red spots in a blue field. Since or- 

 ganisms other than B. coli may also develop red colonies, 

 it becomes necessary further to examine the red colonies 

 in order to prove that they are made up of colon bacilli. 



