PREFACE TO THIRD EDITION xi 



United States, at least, it seems clear that all of the 

 lactose-fermenting group of bacilli are significant of 

 pollution from human or animal sources when present 

 in considerable numbers. The 191 2 report of the 

 Standard Methods Committee apparently takes this 

 view in one place, while retaining the five tests in another 

 section. We have felt it best to place ourselves fairly 

 and fully in Une with the view that the whole group 

 of aerobic lactose-fermenting bacilli is significant and 

 this broad definition is the one upon which we have 

 based our general discussion of the colon group in Chap- 

 ters VI and VII. In Chapter VIII we have discussed 

 the subdivisions of the group as worked out by Mac- 

 Conkey and others and their special significance with 

 respect to recent and remote pollution as suggested by 

 the researches of Houston and Clemesha. 



The use of the lactose-bile test as sufficient evidence 

 of the presence of bacilli of the colon group has become 

 very general and was endorsed by the Laboratory Sec- 

 tion of the American Pubhc Health Association at its 

 191 2 meeting. TheU. S. Treasury Department, acting 

 on the advice of a special commission of experts, in for- 

 mulating a standard for water supplied by common car- 

 riers in interstate commerce has, however, recommended 

 a lactose peptone broth enrichment medium, followed 

 by plate isolation and a confirmatory test in lactose 

 peptone broth. Further study is needed to determine 

 the relative value of these two procedures. 



The growing importance of the application of bac- 

 teriology to the sanitary study of shellfish has led 

 us to include a new chapter dealing with this subject. 



