17 



importation on sailing vessels of infected mosquitoes. These in pro- 

 portion as they found conditions favorable, multiplied more or less 

 rapidly, and abundantly and produced epidemics which were more or 

 less closely confined to, or in the neighborhood of, the shipping. 



Geographic distribution, — The Stegomyia calopus has been found to 

 be one of the most widely distributed of mosquitoes. It is primarily 

 a tropical insect, but has extended north and south along lines of 

 travel, establishing itself permanently wherever the conditions of 

 temperature and moisture are favorable. Speaking broadly, it belts 

 the globe between 38° north and 38° south latitude. 



Within the United States the points at which it has been found, with 

 few exceptions, "fall within the limits of what are known as the 

 tropical and lower austral zones. These life zones include practically 

 all of the southern United States which border on the Atlantic Ocean 

 and the Gulf of Mexico, with the exception of those portions of 

 Virginia, North and South Carolina, Georgia, and Alabama which 

 constitute practically the foothills of the Appalachian chain; in other 

 words, western Virginia and North Carolina, the extreme northwest- 

 ern corner of South Carolina, the northern part of Georgia, and the 

 extreme northeastern corner of Alabama. Further than this, the 

 lower austral zone includes the western half of Tennessee, the western 

 corner of Kentucky, the extreme southern, tip of Illinois, the south- 

 eastern corner of Missouri, and all of Arkansas except the northern 

 portion. It also includes the . southern portion of Indian Territory, 

 southern Arizona, and some of northern Arizona, and southern strips 

 in Utah, Nevada, and California. 



"In the greater part of the territory thus indicated, and where the 

 climate is not too dry, Stegomyia fasciata will, with little doubt, upon 

 close search, be found. 



"All the rest of the lower austral territory just indicated, and where 

 the climate is not too dry, will constitute a region where the yellow- 

 fever mosquito, if once introduced, will undoubtedly nourish. Even 

 in the dryer portions of western Texas, southern New Mexico, south- 

 ern Arizona, southern California, and southern Nevada, where the 

 climate is exceptionally dry, there is a possibility that this species, if 

 once introduced, will breed in the water supply of ranches, except, 

 possibly, where the water is impregnated with alkali.'" 8 



INCUBATION. 



In 29 s cases of experimental yellow fever, recorded in the literature, 

 produced by mosquitoes in nonimmunes that had not been subjected to 



« Howard, 1903. , , mj _ it . . v - 



6 This does not include one case apparently induced by mosquitoes, that had 

 acquired their infection by feeding on sirup in which the bodies of infected mosqui- 

 toes had been crushed. In this case the incubation period would appear to have 

 been not less than 9 nor more than 12 days. 



