152 THE ECONOMIC IMPORTANCE OF ANIMALS 



Method 1. Put a few mosquito larvae and pupae in a small 

 battery jar. Pour in a few drops of kerosene oil. 



Observations. What happens to the oil and the water ? 

 What becomes of the larvae and pupae ? Remembering that all 

 eggs are laid on the surface of the water, what would happen to the 

 eggs when laid? 



Method 2. Place some small goldfish or sticklebacks in a jar 

 containing larvae and pupae. 



Observations. What happens? 



Conclusion. Now go over the map you have made. Which 

 of the above means would you use to exterminate mosquitoes in 

 your locality? 



Problem 126 : To find the relation of mosquitoes to diseases 

 of man. 



NOTE. Malaria and yellow fever, diseases caused by tiny protozoans, are 

 transmitted to man through the bite of mosquitoes. This is proved because men 

 have escaped malaria in malaria-infected districts by taking precautions to have 

 their bodies at all times protected from the bite of the mosquito. This was done 

 by screening, by remaining indoors at times when the mosquitoes were out, and by 

 wearing, when exposed, head nets and gloves. 



In 1890 two London doctors allowed themselves to be bitten by anopheles mos- 

 quitoes which had previously bitten people who had malaria. In a little over two 

 weeks both came down with malaria. 



Observations. What causes malaria? What have swamps 

 and stagnant water to do with malaria? Why did the people 

 who were screened not get malaria ? Why did the London doctors 

 get malaria? 



Conclusion. What has the anopheles mosquito to do with 

 malaria ? 



Problem 127 : To study the life history of tfo parasite caus- 

 ing malaria. 



Material. Charts, or illustration in Hunter's Civic Biology, 

 page 217. 



Observations. Note the lower part of the diagram which 

 represents the blood tube of a man. What changes take place in 

 the parasite within the corpuscles? What two kinds of organisms 

 ultimately are formed? 



