INSECTS AND HEALTH 273 



frightful outbreaks of the fever sometimes occurred in the 

 South. In Havana, Cuba, it was always present. Even 

 there the disease has been stamped out by destroying 

 the mosquitoes (Fig. 178). 



As these mosquitoes breed very extensively in the cis- 

 terns, rain barrels, or other water-holding vessels, the rem- 

 edy evidently consists in removing every unnecessary water 

 vessel and in screening those which must remain with wire 

 screening or cheese cloth so tightly that the mosquitoes can- 

 not get to the water to breed. 



Mosquitoes and malaria. More important than either 

 of the cases which have been mentioned is the relation of 

 mosquitoes to the spreading of malaria. That they do this 

 has been most positively proved, and it is certain that mala- 

 ria is never spread in any other way. The females alone 

 do all of this deadly work, as the males never suck blood. 



How malaria is spread. Malaria is caused by a very 

 minute animal that lives as a parasite in the red blood cells 

 of man. When a mosquito sucks blood from a person 

 who has the disease, the parasites are taken with the blood. 

 In the body of the mosquito certain of them undergo a 

 development which they never do in man. After about 

 ten or twelve days in the mosquito these parasites pass 

 through the stomach walls and gather in its throat. At 

 any time after this occurs, when this mosquito bites a well 

 person, she is likely to force some of the parasites into the 

 person's body along with the saliva which she injects into 

 the wound. In this way, after a few days or weeks, a new 

 case of malaria develops. This is considered as one of 

 the most important recent discoveries in medicine. 



