Now let us sum up some of the reasons why we believe that the malaria fever can be transmitted only through the agency of mosquitoes. First, we know the life-history of the parasite, it has been studied in both of its hosts. Attempts have been made to rear it in other hosts but without avail, and we know from the general relations of the parasite that it must have this sexual as well as the asexual generations. Second, in some regions which would seem to be malarial, that is, where the miasmatic mists arise, no malaria occurs. Why? Usually it can be definitely shown that no _Anopheles_ occur there. Other mosquitoes may be there in abundance, but if no _Anopheles_, there is no malaria. In certain regions this is well demonstrated. 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.