112 ELEMENTS OF GENERAL SCIENCE 



development of a crop of mosquitoes, and it is necessary to 

 give attention to such places in order to avoid danger. 



128. Different kinds of mosquitoes. There are several dif- 

 ferent kinds of mosquitoes. Only one of these, the genus 

 Anopheles, carries the malarial germ. Our most common 

 mosquito ( Culex) does not, so far as we know, carry any dis- 

 ease germ. Yellow fever is produced by another animal germ, 

 carried by the mosquito known as Stegomyia (fig. 57). 



129. Disease germs distributed by other insects. House 

 flies and mosquitoes are not the only insects that transmit 

 diseases. It is known that the germs of bubonic plague are 

 transmitted from person to person by a kind of flea that com- 

 monly lives upon rats. Rats are subject to the plague, and 

 when they die from it the infected fleas leave their bodies 

 and find new hosts. If they alight upon the body of a human 

 being, their bites will probably infect the person with the 

 plague bacteria. Very obviously the disease is much less 

 likely to attack the careful and cleanly person, living in a 

 well-kept dwelling, than it is to attack his less cleanly, 

 vermin-infested neighbor. The only complete protection from 

 this disease and others possibly carried by rats is to be secured 

 by the total destruction of the rat population. The facts men- 

 tioned above explain how it is that in such a country as India 

 the natives may die of the plague in great numbers, while 

 their European neighbors, with cleaner surroundings, usually 

 escape. During the Middle Ages, when all dwellings, from 

 the hovel of the peasant to the palace of the king, were unsan- 

 itary and infested with vermin, epidemics of the plague and 

 other diseases frequently swept Europe, but in modern times 

 nothing of the sort is likely to occur in enlightened nations. 



Various other insects, such as bedbugs, roaches, and certain 

 flies, have been accused, of carrying different diseases. The 

 very deadly spotted fever is carried by a tick, and another 

 tick carries the Texas fever of cattle. 



