826 A BOOK OF INSECTS 



up. Many of the parasites in human blood continue to 

 feed and multiply at the expense of the red corpuscles ; 

 but some of them, after entering corpuscles, do not split 

 up into spores. They become crescent-shaped, and lie 

 dormant. If corpuscles which contain parasites in this 

 condition are sucked up by the right kind of gnat, the 

 crescents continue their development in the insect's 

 stomach — becoming male and female elements. After 

 fertilisation, the females — originally one-thousandth of an 

 inch in diameter — swell up until they are just visible to 

 the naked eye as minute specks embedded in the wall of 

 the gnat's stomach. Ultimately each female, or " sphere," 

 as she may now be called, bursts open and liberates many 

 thousands of the minute needle-like young, which make 

 their way through the insect's blood to its salivary glands. 

 Thence, when the Anopheles bites a man, they pour down 

 through the ducts with the saliva, and thus gain access to 

 the blood of a new victim. 



When once these facts were established, it became 

 clear that in order to combat malaria war must be 

 declared against mosquitoes. These insects must be pre- 

 vented from biting (1) healthy humanity to whom they 

 are likely to convey infection, and (2) malaria- stricken 

 patients from whom they will derive fresh relays of the 

 parasite. As the Anopheles mosquitoes feed chiefly in the 

 evening, or at night, insect-proof houses or beds secure 

 immunity. But the chief aim in malaria-infested countries 

 is to exterminate mosquitoes by destroying their breeding 

 places — draining swamps, and filling up small pools and 

 puddles. If for any reason draining is impracticable, the 

 surface of the water is covered with a thin film of petro- 

 leum. This kills any larva? which may be present when 

 they come up to breathe ; while the adult females, which 

 come to the water to lay their eggs, are also destroyed. 



