DISEASES CAUSED BY PROTOZOA 295 



injects saliva into the blood to break up and digest the red cor- 

 puscles. If the mosquito is infected with malaria, it will inject 

 into the blood at the same time malarial germs which will attack 

 the red corpuscles and begin to grow in them. They grow very 

 rapidly and soon break the corpuscles open, liberating a great 

 quantity of toxin. When this toxin enters the blood from the 

 red corpuscle, it causes chills. 



FIG. 191. 



Courtesy of Am. Mus. Nat. Hist. 



Methods of Preventing Malaria. Quinine is sometimes used to 

 kill malaria germs. Small doses are given da*ily to the patient. 

 The quinine enters the blood and kills the malaria protozoa when 

 it leaves the red corpuscle. 



People living in malaria-infected districts should carefully screen 

 their houses and destroy all places where mosquitoes can breed, such 

 as tin cans, old barrels, and small pools of stagnant water. 



Destroying the Mosquitoes. The mosquito lays its eggs on 

 water. In about a day these hatch into wigglers. These wigglers 

 feed on small one-celled animals that are in the water. They need 

 air to breathe. Hence they come to the surface of the water and 

 thrust out to the air a breathing tube. If the water is covered with 

 oil, they are unable to get this breathing tube through the tough film 

 of oil, and must suffocate. 



It takes from fourteen to seventeen days for the mosquito to 

 reach the "tumbler" stage, so called because instead of wiggling as 

 it swims, it turns over and over. In from ten to twenty days after 

 the egg is laid, the tumbler splits down the back, and the mosquito 

 comes out and flies away. 



