THE COLON BACILLUS 385 



Other media which have been recommended for the differentia- 

 tion of B. coli from JB. typhosus are the Proskauer-Capaldi media 

 and Petruschky's litinus whey, but are not now much used. 



The Proskauer-Capaldi medium No. 1 is an asparagin-mannitol 

 solution with certain salts ; medium No. 2 is a peptone-water - 

 mannitol solution. Both solutions are carefully neutralised and 

 tinged with litmus. 



If these media be inoculated with B. typhosus and B. coli respec- 

 tively and incubated at 37 C. for twenty-four hours, the following 

 changes will be noted : 



Medium No. \. Medium No. 2. 



B. typhosus No growth or change Growth with strongly 



in reaction. acid reaction. 



B. coli . Growth with acid Growth with neutral 



reaction or faintly alkaline 



reaction. 



Petruschky's litmus whey is prepared as follows : Fresh milk is 

 warmed and the casein precipitated by the addition of a minimal 

 amount of hydrochloric acid. It is filtered, and the filtrate of clear 

 whey is carefully neutralised with dilute caustic soda solution. 

 The fluid is then steamed for two hours and filtered ; the filtrate 

 should be clear, colourless, and neutral in reaction. Enough neutral 

 litmus solution is then added to render it well coloured, and the 

 mixture is distributed into test-tubes and sterilised. This medium 

 is rendered slightly acid (represented by 6-10 c.c. N/ 10 caustic soda 

 per cent.) by B. typhosus, very acid (40-50 c.c. ditto) by B. coli. 



The thermal death-point of the organism, according 

 to Weisser and Sternberg, is 60 C. with an exposure of 

 ten minutes. The B. coli will grow freely in a slightly 

 acid medium, and in media containing as much as 0*15 

 per cent, of carbolic acid. In this respect it is a more 

 resistant organism than the B. typhosus. 



Chemical products. The acids produced are mainly 

 laevo-lactic acid with some dextro-lactic acid from glucose, 

 laevo -lactic acid only from mannitol ; also acetic, formic 

 and succinic acids, and alcohol. According to Harden, 

 B. coli attacks glucose in a characteristic manner, each 

 molecular proportion of sugar yielding half a molecular 

 proportion of acetic acid and of alcohol, and one molecular 



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