PREFACE 



The subject of preventive medicine is one that is 

 attracting world-wide attention to-day. We can hardly 

 pick up a newspaper or magazine without seeing the 

 subject discussed in some of its phases, and during the 

 last few years several books have appeared devoted 

 wholly or in part to the ways of preventing rather than 

 curing many of our ills. 



Looking over the titles of these articles and books 

 the reader will at once be impressed with the impor- 

 tance that is being given to the subject of the relation 

 of insects to some of our common diseases. As many 

 of these maladies are caused by minute parasites or 

 microbes the zoologists, biologists and physicians are 

 studying with untiring zeal to learn what they can in 

 regard to the development and habits of these organisms, 

 and the entomologists are doing their part by studying 

 in minute detail the structure and life-history of the 

 insects that are concerned. Thus many important 

 facts are being learned, many important observations 

 made. The results of the best of these investigations 

 are always published in technical magazines or papers 

 that are usually accessible only to the specialist. 



This little book is an attempt to bring together and 



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