PREFACE TO THIRD EDITION 



A SECOND edition of this work was called for in 1908 

 and it was rewritten in that year, with the inclusion 

 of much new material in the chapters dealing with 

 the isolation of the typhoid bacillus and of intestinal 

 bacteria, and with the addition of a new chapter on the 

 bacteriology of sewage and sewage effluents. In the 

 same year there appeared an excellent volume on 

 Water Bacteriology by Dr. W. G. Savage, which showed 

 the English methods of investigation and interpre- 

 tation to be closely in accord with those used in 

 America. 



In the five years which have elapsed since our second 

 edition was published, there has again been important 

 progress along many lines in sanitary bacteriolog}- ; 

 and in particular the publication in 191 2 of a new edition 

 of the Report of the Committee on Standard ^Methods 

 of the Laboratory Section of the American Public 

 Health Association has made necessary a change in 

 many details of current practice. 



We have, therefore, prepared at this time a some- 

 what far-reaching revision of our book. Newer ideas 



