strated. The west coast of Africa is
one of the worst pest-holes of malaria and _Anopheles_. The east coast
has no malaria and no _Anopheles_. In many islands the same condition
exists. On the other hand, the Fiji Islands have _Anopheles_ but no
malaria. No malaria has ever been introduced there to infect the
mosquitoes. In the same way _Stegomyia_ occurs in some of the South Sea
islands and yet there is no yellow fever there.

EXPERIMENTS

We may review, too, a few of the classic experiments that have served to
show that malaria can be contracted in no other way than through the
bite of the mosquito.

For many years Grassi, an Italian, devoted almost his whole time to the
study of malaria. In 1900 he received permission from the government to
experiment on the employees of a piece of railroad that was being built
through a malarial region. This was divided for the purpose of the
experiment into three sections, a protected zone in the middle and an
unprotected zone at each end.

Those working in the protected zone had their houses completely screened
and no one was allowed out of doors after sunset except they were
protected with veils and gloves. Early in the season they were all given
doses of quinine to prevent auto-infection. In the unprotected zone no
screens were used and every one was allowed to go without special
protection. The result for the summer was that there were no new cases
of fever in the protected zone. In the unprotected zones practically all
had the fever as usual.

[Illustration: FIG. 102--Salt-marsh mosquito (_O. lativittatus_)
standing on a table.]

[Illustration: FIG. 103--Anopheles hanging from the ceiling.]

In the same year two English physicians, Sambon and Low, went to Italy
where they built a cabin in one of the marshes noted as being a malaria
pest-hole. The house was thoroughly screened so that no mosquitoes could
enter, but the windows were always open so as to admit the air freely
day and night. Here they lived for three months, out of doors as much as
they pleased during the day but inside where they were protected from
the mosquitoes at night. No quinine was used and no fever developed,
although all about them other people were having the fever as usual.

Another English physician who had not been in malarial regions allowed
himself to be bitten by infected mosquitoes sent from a malarial
locality. In due time he developed the fever. Many other experiments
made in various