300 MOSQUITOES OF NORTH AMERICA 



the United States. Yellow-fever mosquitoes are being brought north of their 

 normal range, escape from their conveyances, find breeding-places, and breed, 

 and it is only necessary that a case of yellow fever be brought to them to enable 

 them to become infected and to start an epidemic. Thus in St. Louis in the 

 year of the Exposition (1904), train service from the south was especially 

 eflScient, and loaded cars came quite to the Exposition gates. Yellow-fever 

 mosquitoes had probably escaped from these cars and bred on the Exposition 

 grounds, as they were found there in August by Mr. A. Busck, of the Bureau of 

 Entomology, who was stationed at the Exposition in charge of the exhibits of 

 the Bureau. 



As has also been pointed out in the section on carriage of mosquitoes by con- 

 veyances, the yellow-fever mosquito has actually extended its permanent range 

 along the railroad running from Vera Cruz up to the City of Mexico by means 

 of railway trains, establishing itself at places where it did not formerly occur, 

 but in which, having the conditions of the moist tropical or moist Lower Austral 

 Zone, it has succeeded in establishing itself in a permanent way. One of the 

 writers' (Howard) observations in 1905, as mentioned in the previous section 

 referred to, were confirmed by the Eeport of Working Party 'No. 1 of the Public 

 Health and Marine-Hospital Service, and the following quotation is from this 

 report : 



" Habitat. — This mosquito is widely distributed, probably more so than any 

 other species, being found throughout the tropical world and well up into the 

 temperate zone. At one time it was supposed to be a coast mosquito, but now it 

 is found to have spread along the commercial lines of communication to cities 

 in the interior that furnish receptacles for breeding places. Its acclimation to 

 the altitudes is gradual, as may be illustrated by the following example : 



" About twenty-eight years ago a railroad was constructed connecting Vera 

 Cruz with the City of Mexico. Some years later a competing line was built be- 

 tween these cities, but going through a different part of the country. Along the 

 line of the Mexican Eailroad yellow fever was unknown in the interior. During 

 the construction of the railroad the disease prevailed among the employees until 

 the road reached the foothills ; it then disappeared. About nine years ago yellow 

 fever appeared in Cordoba at about an altitude of 3000 feet, and has since been 

 epidemic. Three years ago yellow fever appeared at Orizaba and this year 

 (1902) there was a severe epidemic in that city. Since the construction of the 

 railroad many cases of the disease had been received during sickness and con- 

 valescence, and many cases have developed among strangers going through Vera 

 Cruz to that city without the disease in any way affecting the general health of 

 the community, until three years ago. 



" In the second instance, along the line of the Interoceanic Eailroad we know 

 by actual observation that the Stegomyia fasciata has been ascending from 

 station to station until it has now reached Carasal at an altitude of about 3000 

 feet. Synchronously with the ascent of this mosquito yellow fever became epi- 

 demic in those places. El Palmar, the next station above Carasal, about 8 miles 

 distant, does not harbor any of these insects at the present time, and though 

 some cases were sent there from the latter station this last year, there was no 

 spread of the infection. Jalapa, a city of about 35,000 inhabitants, at an altitude 

 of about 4500 feet and about 30 miles above Carasal, does not harbor the Stego- 

 myia fasciata, and though cases have been sent to that place for years from Vera 

 Cruz and intermediate stations, there has never been any spread of the disease. 



