INSECTS IN RELATION TO DISEASE 



323 



malaria patient was dangerous. Mosquitoes raised from the eggs and 

 allowed to sting a person do not cause the disease to appear ; nor does 

 drinking the water in which the mosquitoes develop. Today, nobody 

 who knows the facts can have any doubt as to the relation be- 

 tween the mosquito and the transmission of the disease (see Fig. 152). 



Fig. 152. The malaria parasite 



The parasite attacks the red blood corpuscle of a human being, a, and when it has de- 

 stroyed the corpuscle, J, it breaks up into a large number of spores, e,y;h.ich. may enter 

 other corpuscles and start a new cycle. When blood containing the malaria organism, 

 j, gets into the stomach of a mosquito {Anopheles), the protoplasm undergoes various 

 changes, g, h, resulting in two sexual forms, /', ;', which conjugate and produce a fer- 

 tilized egg, k. This works its way into the wall of the insect's stomach, /, and breaks 

 up into a large number of tiny bodies, m, which finally lodge in the insect's salivary 

 glands, n. When the insect again stings a person, some of these bodies, 0, get into the 

 victim's blood and find their way into the red corpuscles, <z, and the cycle begins again. 

 p is the stomach of infected mosquito, showing swellings produced by the parasite 



The most common mosquitoes found in various parts of this country 

 belong to the genus Cnlex. This is a nuisance, but so far as is now 

 known it does not transmit any disease to human beings (see Fig. 153). 



