X Preface 



lems of self purification in Chapter I, to the description 

 of methods for the isolation of the typhoid bacillus in 

 Chapter V, to the treatment of the interpretation of the 

 colon test in Chapter VII, to an account of the newer 

 presumptive tests for B. coli in Chapter VIII, and to 

 the discussion of the significance of intestinal bacteria, 

 other than B. coli, in Chapter IX. A new chapter has 

 been introduced on The Bacteriology of Sewage and 

 Sewage Effluents, in recognition of the growing impor- 

 tance of this branch of the subject. 



The Biological Laboratories, 



Massachusetts Institute of Technology, 



Boston, January i, igoS. 



