INTRODUCTION 7 



result in a vast improvement in the sanitary conditions of 

 our towns and cities, and consequently in the health of the 

 inhabitants. 



The desirability of applying such measures in camps and 

 temporary collections of dwellings, where large bodies of men 

 are brought together, cannot be too strongly urged. 



CHAPTER II 



THE SPECIES OF NON-BLOOD-SUCKING FLIES 

 FOUND IN HOUSES 



In some tropical and subtropical countries house-flies {Musca 

 domesticd) are extraordinarily abundant, and the natives take so 

 little notice of them that not only children but adults allow flies 

 to settle in swarms about their eyes and seldom make any 

 attempt to drive them away. Ophthalmia is common and 

 under the conditions which prevail flies probably carry the 

 germs directly from one person to another. In other parts of 

 the world various species of flies appear to transmit the virus of 

 yaws (Chapts. XVIII, xix) in a similar manner. In temperate 

 climates, however, the direct transference of disease germs from 

 one individual to another cannot be so common, for the in- 

 habitants of these countries have not acquired the same degree 

 of indifference to the presence of flies on their persons. In 

 these countries they are more likely to transmit disease by 

 contaminating articles of food. 



Since this book is mainly concerned with the danger from 

 flies in temperate countries it has been thought best to consider 

 first those species of non-biting flies which frequent houses and 

 shops, w^here articles of food are exposed for sale. 



The majority of non-biting flies, which at present appear to 

 be of importance in the transmission of disease, belong to the 

 Sub-order Cyclorrhapha of the Order Diptera, or two-winged 

 flies. 



