PREFACE ix 



the scope of this book and bibliography not directly 

 referred to here. 



Most of the above mentioned works, excellent as 

 they are, are difficult for any except those with a 

 fair knowledge of the subject already and the most of 

 them are of more service to biologists than to prac- 

 titioners in preventive and curative medicine. 



The confusion w^hich still exists, almost as great 

 as ever among those most practically concerned with 

 the subject, has been the stimulus in attempting 

 this book. 



It has been planned as a monograph for students 

 and practitioners of medicine and for those variously 

 connected with medicine in special ways which bring 

 them as responsible parties into this very common 

 consideration in the diagnosis, prevention and treat- 

 ment of disease in man. 



It is not intended for protozoologists, save as a 

 connecting link between their science and medicine. 

 To biologists it will be an unconventional book. It 

 is purposely so. Technical details which tend to con- 

 fuse and so lose the interest of those to whom they 

 are of no concern are largely left out of considera- 

 tion. 



To many medical practitioners it will probably be 

 a radical book. In my several years of experience as 

 a sort of a go-between in protozoology and medicine 

 I have come to some very definite opinions as to cer- 

 tain practices in medicine which are difficult to jus- 

 tify. These conclusions may not be agreeable to 

 certain practitioners. 



