4 INTRODUCTION 



for the spread of typhoid, but, considering that the creature is 

 dangerous from every point of view, and that it is an important 

 element in the spread of typhoid, it seems advisable to give it 

 a name which is almost wholly justified and which conveys in 

 itself the idea of serious disease. Another repulsive name that 

 might be given to it is ' manure fly,' but recent researches have 

 shown that it is not confined to manure as a breeding place, 

 although perhaps the great majority of these flies are born in 

 horse manure. For the end in view, ' typhoid fly ' is considered 

 the best name." 



In the United States this name has been very generally 

 adopted in the newspapers, and " it is undoubtedly true that 

 people will fear and fight an insect bearing the name ' typhoid 

 fly,' when they will ignore one called the 'house-fly,' which they 

 have always considered a harmless insect." 



Hewitt (1912, p. 106) states that "it has been proved that 

 the house-fly plays an important part in the dissemination of 

 certain of our most prevalent infectious diseases, when the 

 necessary conditions are present," and Nuttall and Jepson (1909) 

 regard the evidence relating to the spread of cholera and 

 typhoid fever as " quite convincing." 



Hitherto the house-fly {Musca doinestica) has been mainly 

 investigated since it occurs in all parts of the world, and is the 

 species which is most commonly found in and round houses. 

 Many other species, however, occasionally enter houses, or places 

 where food is exposed for sale, and possibly act as carriers of 

 disease. In regard to most of these little is known. 



Up to the present the following facts have been definitely 

 ascertained. The larvae of many species of non-biting flies 

 breed in human and animal excreta, or decaying animal and 

 vegetable matter, and the adults frequent these substances and 

 often feed upon them. Flies are therefore an indication of the 

 presence of such insanitary substances in the neighbourhood of 

 the houses in which they occur. They carry both in and on 

 their bodies the putrefactive and faecal bacteria acquired from 

 the substances on which they feed, and, experimentally at least, 

 can also carry and distribute many of the disease producing 

 species of bacteria and the ova of parasitic worms. Since these 



