PREFACE TO THIED 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 1912 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 line with the view that the whole group 

 of lactose-fermenting bacilli is significant and that 

 the lactose bile fermentation test is a sufficient identi- 

 fication of the colon group for ordinary sanitary pur- 

 poses. This broad definition is the one upon which 

 we have based our general discussion of the colon 

 group in Chapters VI and VII. In Chapter VIII 

 we have discussed the subdivisions of the group as 

 worked out by MacConkey and others and their special 

 significance with respect to recent and remote pollu- 

 tion as suggested by the researches of Houston and 

 Clemesha. 



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, 

 based largely upon the recent report of the Committee 

 of the Laboratory Section of the American Public 

 Health Association. 



Throughout the book we have resorted freely to 

 the use of tables of actual data for the illustration of 

 the various points discussed, believing that ample 

 familiarity with practical examples furnishes the only 

 sound basis for judgment in sanitary water exam- 

 ination. 



