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 
efficient, 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 Report 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 Railroad 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 Railroad 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 20 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. 
