17 



that over 99 per cent of the flies found in kitchens and dining rooms 

 and attracted to food supplies are house flies, there are a few others 

 which are attracted to and which may breed in human excrement that 

 also have to be guarded against, and as these do not breed in horse 

 manure the treatment just described will not be effective against them. 

 The care of human excrement, however, will prevent the carriage of 

 typhoid germs even by these species. The little fruit flies of the 

 genus Drosophila (fig. 10), which breed in overripe or decaying fruit, 

 are the principal species in this category. Therefore, fruit store- 

 houses or fruit receptacles should be screened, and overripe fruit 

 should not be allowed to remain in dining rooms or kitchens for any 

 length of time. 



OTHER DISEASES CARRIED BY INSECTS. 



While in malaria and typhoid we have the two principal diseases 

 common to the United States which may be conveyed by insects, the 



Fig. 14.— Black gadfly— enlarged (original). Fig. 15.— Bedbug— enlarged, (after Marlatt). 



agency of these little creatures in the transfer of disease germs is 

 much more widespread in warm countries, and it is by no means con- 

 fined to human beings. In Egypt and in the Fiji Islands there is a 

 destructive eye disease of human beings the germs of which are carried 

 by the common house fly. In our Southern States an eye disease 

 known as pink-eye is carried by certain very minute flies of the genus 

 Hippelates. In certain tropical countries a disease known as filariasis, 

 which somewhat resembles certain forms of leprosy, is transferred 

 among human beings by certain mosquitoes. There is good reason to 

 suppose that the germs of the bubonic plague may be transferred 

 from sick people to healthy people by the bites of fleas (fig. 11). 

 The so-called Texas fever of cattle is unquestionably transferred by 

 the common cattle tick (fig. 12), and this was the earliest of the 

 clearly demonstrated cases of the transfer of disease by insects. In 

 25338— No. 155—02 2 



