, and other Spanish-American seaports; also on the west coast
of Africa. It is frequently epidemic in the tropical ports of the
Atlantic in America and Africa, and there have been numerous epidemics
in the southern and occasional ones in the northern seacoast cities of
the United States. The last epidemic occurred in the South in 1899.
Rarely has the disease been introduced into Europe, and it has never
spread there except in Spanish ports. The disease is one requiring
warm weather, for a temperature under 75 deg. F. is unsuitable to the
growth of the special mosquito harboring the yellow-fever parasite. It
spreads in the crowded and unsanitary parts of seacoast cities, to
which it is brought on vessels by contaminated mosquitoes or
yellow-fever patients from the tropics. Havana has heretofore been the
source of infection for the United States, but since the disease has
been eradicated by the American army of occupation, that danger has
been removed. Yellow fever is not at all contagious in the sense that
a healthy person can contract the disease by contact with a
yellow-fever patient, or with his discharges from the stomach, bowels,
or elsewhere, and is probably only communicated to man by the bite of
a particular kind of mosquito harboring the yellow-fever organism in
its body. Both these facts have been incontestably proved,[12] in part
by brave volunteers from the United States Army who submitted to sleep
for twenty-one days on clothes soiled with discharges from patients
dying of yellow fever, and escaped the disease; and by others living
in uncontaminated surroundings who permitted themselves to be bitten
by infected mosquitoes and promptly developed yellow fever.

=Development.=--After a person has been bitten by an infected
mosquito, from fourteen hours to five days and seventeen hours elapse
before the development of the first symptoms--usually this period
lasts from three to four days. With the appearance of a single case in
a region, a period of two weeks must elapse before the development of
another case arising from the first one. This follows because a
mosquito, after biting a patient, cannot communicate the germ to
another person for twelve days, and two days more must elapse before
the disease appears in the latter.

=Symptoms.=--During the night or morning the patient has a chill (or
feels chilly) and experiences discomfort in the stomach, with
sometimes nausea and vomiting. There is pain through the f