324 



BIOLOGY AND HUMAN LIFE 



245. Yellow fever. This disease, which has been in the past much 

 more fatal than malaria, is found only in tropical or semitropical regions, 

 although there have been epidemics of yellow fever as far north as Phila- 

 delphia, New York,^ and Boston. At the close of the Spanish-American 



War, while the parasite that 





Eggs 



LarocB 



Pupoe 



causes the disease was still 

 unknown, a commission of 

 American physicians defi- 

 nitely proved that the mos- 

 quito Stegomyia fasciata, 

 now called Aedes (pro- 

 nounced in three syllables) by 

 the entomologists, was really 

 the intermediary in the trans- 

 mission of the disease, as had 

 long been suspected by many 

 students of the problem. 

 The commission consisted of 

 Dr. Walter Reed, Dr. James 

 Carroll, and Dr. Jesse W. 

 Lazear ; they were assisted 

 by a Cuban, Aristide Agra- 

 monte, who had recovered 

 from the disease and was 

 therefore immune. In one of 

 the two cottages used the 

 ventilation was intentionally 

 very poor ; in the other there 

 was a mosquito-tight screen 

 separating the two halves, 

 and the ventilation was very 

 good (see Fig. 154). Both 

 cottages were well screened 

 to prevent the entrance or 

 escape of mosquitoes. In the 

 first cottage three volunteers 

 received cases of clothing and bedding from men who were suffering 

 from yellow fever or who had died with the disease. They shook out 

 these contaminated articles and slept in the soiled garments and in 

 the soiled bedclothes for twenty days. Not one became infected. 

 This experiment was repeated two times more, with no results to show 



Adults 



Culex Anopheles 



Fig. 153. 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 paral- 

 lel to the resting surface, whereas in Anopheles 

 the hind end of the body is farther from the 

 resting surface than the head 



