THE COLON GROUP OF BACILLI 



123 



the isolation of sewage bacteria. Jackson studied 

 the action of various bile media and showed their 

 selective inhibitory action in the striking table quoted 

 below. His important contribution to the subject, 

 however, was the discovery that ox bile itself could 

 be used as a culture medium, and that it was easier 

 to prepare, cheaper and more effective than combina- 

 tions of meat infusion with the purified bile salts. 



SELECTIVE ACTION OF BILE SALTS 

 (Jackson, 1906) 



* Bile diluted, i : i. 



Jackson suggested the use of fresh ox bile containing 

 I per cent of lactose as a presumptive test instead of 

 dextrose broth. In particular he hoped that this medium 

 would be free to a great degree from the negative results 

 due to overgrowths in polluted waters. He reported 

 275 examinations of badly contaminated waters, in 

 which 65 per cent of the samples failed to give the 

 dextrose-presumptive test, and only 10 per cent failed 

 to show gas in lactose bile. In a more recent communica- 

 tion, Jackson (1907) reports that in the examination of 



