iSS 
Arthropods as Hosts of Pathogenic Protozoa 
The clearest early presentation of the circumstantial evidence in 
favor of the theory of mosquito transmission was that of A. F. A. 
King, an American physician, in 1883. He presented a series of 
epidemiological data and showed “how they may be explicable by 
the supposition that the mosquito is the real source of the disease, 
rather than the inhalation or cutaneous absorption of a marsh vapor.” 
We may well give the space to summarizing his argument here for 
it has been so remarkably substantiated by subsequent work: 
1. Malaria, like mosquitoes, affects by preference low and moist 
localities, such as swamps, fens, jungles, marshes, etc. 
2. Malaria is hardly ever developed at a lower temperature 
than 6o° Fahr., and such a temperature is necessary for the develop¬ 
ment of the mosquito. 
3. Mosquitoes, like malaria, may both accumulate in and be 
obstructed by forests lying in the course of winds blowing from 
malarious localities. 
4. By atmospheric currents malaria and mosquitoes are alike 
capable of being transported for considerable distances. 
5. Malaria may be developed in previously healthy places by 
turning up the soil, as in making excavations for the foundation of 
houses, tracks for railroads, and beds for canals, because these opera¬ 
tions afford breeding places for mosquitoes. 
6. In proportion as countries, previously malarious, are cleared 
up and thickly settled, periodical fevers disappear, because swamps 
and pools are drained so that the mosquito cannot readily find a place 
suitable to deposit her eggs. 
7. Malaria is most dangerous when the sun is down and the 
danger of exposure after sunset is greatly increased by the person 
exposed sleeping in the night air. Both facts are readily explicable 
by the mosquito malaria theory. 
8. In malarial districts the use of fire, both indoors and to those 
who sleep out, affords a comparative security against malaria, because 
of the destruction of mosquitoes. 
9. It is claimed that the air of cities in some way renders the 
poison innocuous, for, though a malarial disease may be raging out¬ 
side, it does not penetrate far into the interior. We may easily 
conceive that mosquitoes, while invading cities during their nocturnal 
pilgrimages will be so far arrested by walls and houses, as well as 
attracted by lights in the suburbs, that many of them will in this 
way be prevented from penetrating “far into the interior.” 
