406 



ELEMENTARY BIOLOGY 



Larvce, 



son of Dr. Manson who had never suffered from the disease, and 

 who lived in a region where there were no cases of malaria, allowed 

 themselves to be stung by the suspected mosquitoes. In the course 



of a few days both developed 

 the characteristic symptoms 

 of the disease. This experi- 

 ment showed that the night 

 air and the vapors from the 

 swamps of the Campagna 

 were harmless, and that the 

 sting of a mosquito that had 

 once bitten a person with 

 malaria was dangerous. Mos- 

 quitoes raised from the eggs 

 and allowed to sting a per- 

 son do not cause the dis- 

 ease to appear. Drinking the 

 water in which the mosqui- 

 toes developed does not cause 

 the disease to appear. These 

 conclusions were later con- 

 firmed by further experi- 

 ments, so that to-day there 

 can be no doubt as to the 

 relation between the mos- 

 quito and the transmission 

 of the disease (see Fig. 209). 

 The most common species 

 of mosquito found in various 

 parts of this country belong 



Culex Anopheles 



FIG. 210. Mosquito life histories 



The mosquitoes of the genus Anopheles, which 

 transmit malarial parasites, differ from the com- 

 mon Culex in every stage. We can readily dis- 

 tinguish the adults of the two genera by the fact 

 that when at rest the Culex holds its body parallel 

 to the resting surface, whereas in Anopheles the 

 hind end of the body is farther from the resting 

 surface than the head 



to the genus Culex. This is a 

 nuisance, but, so far as known, 

 does not transmit any disease 

 to human beings (Fig. 210). 



441. Yellow fever. This disease is found only in tropical or semi- 

 tropical regions, although there have been epidemics of yellow fever 

 as far north as Philadelphia, New York, and Boston. It has been in 

 the past a much more fatal disease than malaria, and turns out to be 

 carried by certain species of mosquito. While the parasite that causes 



