206 Nature-Study Agriculture 



Louis Harvey 



FIG. 160. Building a fence along the border to keep out Mexican cattle, which 

 are often infected with fever ticks. 



rats to men, human beings are in danger wherever there 

 are any infected rats (Fig. 161). A few years ago the 

 city of San Francisco spent many thousands of dollars 

 in destroying rats among which the plague had spread. 

 Mosquitoes The mosquito may be regarded as a parasite, for it 

 malaria secures its living in part, at least, by sucking the blood 

 of animals, while the juices of plants also furnish it with 

 food. The male mosquito has not a beak strong enough 

 to pierce the skin of an animal, and he must rely upon 

 plants for all his food. Many kinds of mosquitoes are 

 quite harmless, except that they take a drop of our 

 blood now and then. But one kind was the carrier of 

 yellow fever until that disease and the mosquito that 

 kept it going were practically stamped out together. 

 Another kind, the Anopheles, is the carrier of malaria. 

 If an Anopheles mosquito bites a person suffering from 

 malaria, it draws the disease germs into its own body. 



