12 THE YELLOW-FEVER MOSQUITO. 
out of water a considerable time, and the pupe show great resistance 
to drying. Experiments made by Peryassu in Brazil showed that 
when larve were placed upon filter paper none lived nine hours. 
When placed upon moist ground, according to temperature and 
evaporation, they survived as much as 13 days, and when again put 
in water developed to imagoes. Pupe dried upon filter paper sur- 
vived up to 9 hours and 30 minutes. 
GEOGRAPHIC DISTRIBUTION. 
In considering the geographic distribution of the yellow-fever 
mosquito it should be pointed out at the start that it has two dis- 
tinct regions—one in which it is capable of breeding continuously 
and another over which it, spreads during warm weather, to be an- 
nually exterminated by cold after breeding for an indefinite number 
of generations. The first may be termed the permanent region and 
the second the temporary summer region. The permanent distribu- 
tion is limited in a general way by the frost line. Where frost does 
not occur the species generally may breed permanently. As has been 
already shown, this mosquito does not thrive below a temperature of 
80° F., so that in a uniform climate with a temperature much below 
80° the species will not continue to exist. Such climates are rare, 
however, in regions where frost never occurs. 
The temporary summer distribution is determined by the means of 
carriage that happen to be available. It has been shown that the 
yellow-fever mosquito is a domestic species, having a fairly long 
life in the adult stage and having the custom of hiding itself in_ 
the most ingenious ways. It is therefore particularly subject. to 
carriage for long distances on board vessels, in railway trains, and 
even packed securely away in baggage. In the old days of sailing 
vessels on very long voyages it was not only possible for the yellow- 
fever mosquito to breed continuously in the more or less exposed 
water supply of vessels, but undoubtedly this was of common occur- 
rence. Every year it is carried to the north in the United States 
upon railway trains and may breed for a generation or so hundreds 
of miles north of its permanent breeding places. Thus while the 
species breeds permanently only in the extreme southern portion of 
the United States, it will be found every summer breeding for a 
generation or so in localities to which it has been carried by trains. 
In 1904, for example, it was found breeding abundantly upon the 
erounds of the St. Louis exposition, and had one or more persons 
suffering with incipient yellow fever come to the exposition, the 
mosquitoes were there in numbers to carry the disease. Everywhere 
almost throughout the southern United States in midsummer will 
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