2 INTRODUCTION 



or poliomyelitis. One by one man's parasitic attendants and 

 blood-sucking visitors have been shown to be potent vehicles of 

 death. Of all revelations perhaps none affects so great a number 

 of people in all countries, both by its significance and effects, as 

 the demonstration of the disease-carrying power of the common 

 house-fly. From the dark ages man has been accustomed to 

 regard his ubiquitous companion in his wanderings over the face 

 of the globe, not only with a marked degree of tolerance, but, 

 if the rhymes of our childhood are to be believed, with some 

 measure of affection. The discovery, therefore, of the fact that 

 the commonest and most widely distributed insect and the animal 

 most closely associated with man was not only begotten and a 

 frequenter of filth, but was also a potent and common carrier of 

 pathogenic and putrefactive organisms, excited an interest in the 

 minds of a larger number of people than many other discoveries 

 of a like character in which both the insect and the disease with 

 which it was associated were more restricted in their distribution 

 and affected a correspondingly small number of people. 



So obsessed were people's minds with the idea that the 

 house-fly was of no significance in relation to man's welfare that 

 it was not only deemed unworthy of serious study, but when, 

 as a result of close study, its true character and habits were 

 being revealed, the results of such studies were regarded with 

 considerable surprise and scepticism. The story of the gradual 

 revelation of the disease-carrying powers of the house-fly is 

 recorded in subsequent chapters. The history of the develop- 

 ment of our knowledge of the insect itself, its structure, habits 

 and life-history is noteworthy on account of our long continued 

 ignorance concerning these facts. 



Naturalists of all ages have briefly referred to the habits ant 

 characteristics of the house-fly. Both Reaumur (1738) and De Gee' 

 (1758-78) included short accounts of this insect in theii' classica 

 memoirs, but they contributed little to our knowledge of th> 

 structure or development of the fly. 



The most comprehensive of the earlier accounts of the hou" 

 fly was written b}' Gleichen (1790)\ This most interesting b 



1 This is the diite of the copy of this rare book which is in my possession ; t,]^ 

 niay have been, liowever, an earlier edition in 1766. 



