670 TEANSMISSION OF YELLOW FEVER BY MOSQUITOES. 



accumultite in pools, as well as open cesspools to serve as ])reedinfr 

 places for Culex f<wckitus^ that city will present conditions more 

 favorable for the propagation of yellow fever than it would if well- 

 paved and drained and sewered. 



The question whether yellow fever may be transmitted by any other 

 species of mosquito than Oulex fasciatus has not been determined. 

 Facts relating- to the propagation of the disease indicate that the mos- 

 quito which serves as an intermediate host for the yellow-fever germ 

 has a somewhat restricted geographical range and is to be found espe- 

 cially upon the seacoast and the margins of rivers in the so-called 

 "yellow-fever zone." While occasional epidemics have occurred 

 upon the southwest coast of the Iberian peninsula, the disease, as an 

 epidemic, is unknown elsewhere in Europe, and there is no evidence 

 that it has ever invaded the great arid populous continent of Asia. 

 In Africa it is limited to the west coast. In North America, although 

 it has occasionally prevailed as an epidemic in ever}' one of our sea- 

 port cities as far north as Boston, and in the Mississippi Valley as far 

 north as St. Louis, it has never established itself as an endemic dis- 

 ease within the limits of the United States. Vera Cruz, and probably 

 other points on the Gulf coast of Mexico, are, however, at the present 

 time endemic foci of the disease. In South America it has prevailed 

 as an epidemic at all of the seaports on the Gulf and Atlantic coasts, 

 as far south as Montevideo and Buenos Ayres, and on the Pacific 

 along the coast of Peru. 



The region in which the disease has had the greatest and most fre- 

 quent prevalence is bounded b}' the shores of the Gulf of Mexico, and 

 includes the West India Islands. Within the past few years yellow 

 fever has been carried to the west coast of North America, and has 

 prevailed as an epidemic as far north as the Mexican port of Guaymas, 

 on the Gulf of California. 



It must not be supposed that Culex faseuttus is only found where 

 yellow fever prevails. The propagation of the disease depends upon 

 the introduction of an infected individual to a locality where this mos- 

 quito is found, at a season of the year when it is active. Owing to 

 the short period of incubation (live days or less), the brief duration of 

 the disease, and especially of the period during which the infectious 

 agent (germ) is found in the blood, it is evident that ships sailing from 

 infected ports, upon which cases of yellow fever develop, are not 

 likely to introduce the disease to distant seaports. The continuance 

 of an epidemic on shipboard, as on the land, nuist depend upon the 

 presence of infected mosquitoes and of nonimmune individuals. Under 

 these conditions we can readily understand why the disease should not 

 be carried from the West Indies or from South America to the Medi- 

 terranean, to the east coast of Africa, or to Asiatic seaport cities. On 

 the other hand, if the disease could be transmitted by infected cloth- 



