Vi PREFACE. 



but these are by no means exhaustive, many had to be omitted 

 with regret. The hygienic examination of milk has been 

 practically rewritten; the hygienic examination of water con- 

 siderably expanded. The chapter on disinfectants, and that 

 on surgical antisepsis have been also greatly altered. The 

 interesting theoretical subject of the diversion of complement 

 has been added to the chapter on immunity. The trypano- 

 somes and the amoeba have been given additional space, but 

 certainly not more than these increasingly important micro- 

 organisms demand. The index has been not only greatly 

 enlarged, but the references have been made much fuller and 

 more specific. 



A very full card catalogue of references prepared by 

 Dr. Williams was made use of in looking up most of the 

 articles which have been cited. 



As in the fourth edition, the author is relieved of all 

 responsibility for the statements made in the present edition; 

 both for those retained from former editions, as well as for 

 those which have been added by the reviser. 



B. MEADE BOLTON. 



WASHINGTON, D. C., 



