PREFACE TO THE SECOND EDITION. 



The preparation of this edition has furnished us with the 

 opportunity of enlarging and improving the arrangement 

 of several of the articles, and of submitting the whole to 

 thorough revision. In the first edition we avoided insert- 

 ing references to foreign publications, but, as in many 

 cases readers may desire to refer to such, we have now 

 frequently given them. 



In view of the growing importance of bacterial methods 

 of sewage treatment, we have included a short account of 

 the bacteriology of sewage. 



We have great pleasure in acknowledging our indebted- 

 ness to Dr. Patrick Manson for kindly revising the article 

 on Malaria, also to Dr. Ladds, Mr. F. W. Stoddart, and 

 others, for kind assistance. T. H. P. 



C. G. M. 



May 1st, 1898. 



