STEGOMYIA F ASCI AT A. 715 



my ia fas data has been found capable of transmit- 

 ting the disease, and analogies suggest the proba- 

 bility that no other insect is concerned. 



These discoveries explain many facts in rela- Epidemiology 

 tion to yellow fever which had been obscure hither- 

 to. For example, yellow fever is a tropical and 

 subtropical disease only because Stegomyia fas- 

 ciata breeds in tropical and subtropical climates. 

 The disease is found in low, moist localities rather 

 than in the high and dry, because the mosquito in- 

 habits the former and not the latter. Yellow 

 fever dies out with the first severe frost or on the 

 advent of cool weather because these conditions 

 either kill the mosquito or cause him to hibernate. 

 The advent of an initial case of yellow fever in a 

 suitable region is followed by the appearance of the 

 disease in epidemic form only after a period of two 

 or three weeks, because the mosquito first becomes 

 infectious in about two weeks after it has fed on 

 yellow fever blood; this may correspond with a 

 certain stage of development of the as yet unrecog- 

 nized parasite. The observation often made that 

 yellow fever, like malaria, is not contagious in the 

 ordinary sense, in spite of its rapid extension, is 

 readily understood, as is the irregular method in 

 which the disease spreads. It is now clear why the 

 disinfection of fomites has never been able to 

 check the advance of an epidemic, and why the 

 ordinary quarantine measures which did not take 

 the mosquito into consideration were not effective 

 in keeping the disease out of a favorable port ; and 

 by a favorable port is meant one which can harbor 

 Stegomyia fasciata. These discoveries also ex- 

 plain how yellow fever could be stamped out of 

 Havana, Texas and New Orleans by prophylactic, 



