53 



is best to discount the presence 'of attenuated Fact, coli and to be sure to 

 obtain all vigorous types. The lactose bile medium accomplishes both these 

 objects." 



This contention, that bile affects the weaker strains, must be regarded 

 merely as an assumption, for it is not substantiated by actual observations. 

 Jordan, in a careful study of the subject, concludes that there is no re- 

 lation between attenuation and the antiseptic action of the bile. He found 

 that freshly isolated strains were inhibited to as great or even greater 

 degree than old strains. Gumming, in a comparison of lactose bile and 

 lactose broth, found that with sewage preliminary enrichment in lactose 

 bile yielded only 25 percent as many colon forms as were obtained with 

 lactose broth. In a similar study with river water, the bile method gave 

 50 to 70 percent as many colon organisms as the broth. These results 

 would indicate quite the converse of the contention of the 1912 report of 

 the Committee on Standard Methods that "Attenuated B. coli does not re- 

 present recent contamination, and all B. coli not attenuated grow readily 

 in lactose bile." 



The 1917 and 1920 reports of the Committee on Standard Methods of 

 Water Analysis recommend the use of lactose broth for preliminary en- 

 richment and the presumptive test on the ground tha it gives a higher total 

 number of positive isolations. The concensus of opinion at present seems 

 to be in favor of the substitution of broth for bile. 



Lactose Broth vs. Lactose Bile. Jordan in 1913 called attention 

 to the greater proportion of successful isolations of T act. coli with lactose 

 broth. Of forty 5 c. c. portions of Lake Michigan water inoculated 

 into lactose broth and lactose bile media, colon bacilli were isolated from 

 42 percent of the former and only 30 percent of the latter. Similarly one 

 hundred and fifty 1 c. c. samples yielded 31 percent positive isolations 

 with lactose broth compared to 22 percent when lactose bile was em- 

 ployed for preliminary enrichment. 



Creel in a study of drinking waters on railroad trains reports the 

 following frequencies of the colon group in comparative tests: 



Water samples containing colon group 91 



Positive from lactose bile only 18 



Positive from lactose broth only 45 



Positive from both media 27 



The inhibitory action of the bile is very marked. About 50 percent 

 of the colon bacilli isolation would have been lost if reliance had been 

 placed on lactose peptone bile alone. 



Similarly Dr. Gumming in the Potomac River studies calculates the 

 number of colon bacilli to be 84 per c. c. by lactose broth enrichment 

 followed by confirmatory tests as compared to 47 when lactose bile was 

 employed and followed by confirmatory tests, again indicating that about 

 half of the colon bacilli were lost when preliminary enrichment was car- 

 ried out in the bile medium. 



Obst comes to the same conclusion. Houser of the Cincinnati Water 

 Supply prefers the broth medium. Ritter in a detailed comparison of 



