17 



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 

 b}^ 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 tropi- 

 cal countries a disease known as 

 filariasis, which somewhat resem- 

 bles 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 trans- 

 ferred 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 

 Africa a similar disease of cattle is transferred by the bite of the 

 famous biting fly known as the tsetse fly (fig. 13) and the so-called 



Fig. 11.— Cat 



and dog flea, 

 (original). 



Enlarged 



Fig. 12. — Cattle tick. Enlarged (redrawn from Salmon and Stiles). 



" sleeping sickness " of human beings is conveyed by the same insect. 

 The germs of the disease of cattle known as anthrax are carried by 

 gadflies, or horse flies, and when these flies subsequently bite human 

 beings malignant pustules may result (see fig. 14 for one of these 

 gadflies) ; and other discoveries of this nature are constantly being 



155 



