THE YELLOW-FEVER MOSQUITO. 13 
this mosquito be found, and this explains why epidemics of yellow 
fever have occurred in years past on the Atlantic coast of North 
America even as far north as Montreal. 
On the Pacific coast, on the other hand, the nights are so cold that 
this species does not seem to be able to survive. This applies to 
points north of San Diego. The species breeds permanently in all 
of the west coast Mexican seaports, and must frequently be brought 
to the California coast in vessels, but it has never been known to 
‘breed there. This seems at first sight strange, since the mean annual 
temperature of California is much above that of eastern cities where | 
epidemics have occurred, and in San Diego and Los Angeles one sees 
tropical vegetation on every hand growing unprotected, and severe 
cold is unknown; yet the nights are cold even in the summer, and it 
is to this condition—the low minimum nightly temperatures—that 
freedom from the yellow-fever mosquito, and consequently from 
yellow-fever epidemics, is due. 
ORIGINAL HOME. 
The original home of the yellow-fever mosquito must clearly be 
identical with that of yellow fever. Early history points very 
strongly to the West Indies and the adjacent mainland as that original 
home. There has been much discussion of the question, and ingenious 
arguments have been adduced to prove that yellow fever is of African 
origin and was imported into America through the slave trade. All 
things considered, however, the probabilities are that yellow fever 
is one of the very old diseases of mankind in the New World, and 
that it was taken from the New World to the Old. 
DISCOVERY OF THE RELATIONS OF THIS MOSQUITO TO YELLOW 
FEVER. 
Physicians had been theorizing about the cause of yellow fever from 
the time when they began to treat it. It was thought by many that 
it was carried in the air, by others that it was conveyed by the cloth- 
ing, bedding, or other articles which had come in contact with yellow- 
fever patients. There were one or two early suggestions of the 
agency of mosquitoes, but practically no attention was paid to them, 
and they have been resurrected and considered significant only since 
the beginning of the present century. 
With the discovery of the agency of microorganisms in the causa- 
tion of disease, a search soon began for some causative germ of yellow 
fever. Many microorganisms were found in the course of autopsies 
and many claims were set forth by investigators. All of these, how- 
ever, were virtually set at rest by Sternberg in his “ Report on the 
BAT 
