
INSECTS AND DISEASE 
It had been noted that ‘‘malaria is freely generated at the bases 
of mountain ranges in tropical climates,’ that “temperature exercises 
Sreat influence over its development and activity,’ ““many places can 
be visited with impunity in winter which are dangerous in summer 
and autumn”; that “malaria drifts along plains to a considerable 
distance from its source, when aided by winds sufficiently strong to 
propel, but not to dispel it’’; that ‘“‘under the influence of currents 
of heated air it can ascend, in dangerous concentration, far above its 
source’; that ‘‘a belt of forest interposed between any malarial place 
and human habitations affords considerable protection.”’ 
Could anything be more mysterious than this picture? Yet 
only three years after this article appeared in Quain’s Encyclopedia 
the mystery was solved. 
The germ of malaria, a Protozoan parasite which destroys the 
red cells of the blood, had been first seen by a French surgeon, 
Laveran, in 1880, and an individual observer here and there had 
suggested a possible connection between malaria and mosquitoes. 
In 1883 an American, A. F. A. King, had urged with special force 
the hypothesis that ‘“‘the mosquito is the real source of the disease 
rather than the inhalation or cutaneous absorption of a marsh 
vapor.” 
It was only in the early nineties, however, that the proof of this 
assumption was at last furnished. Patrick Manson and Ronald Ross, 
two English physicians, at that time began serious work on the 
mosquito theory and in 1897 Ross discovered the germ of bird 
malaria in the stomach of the mosquito. The Italians, Grassi and 
Bignami, first demonstrated the germ of human malaria in the body 
of the mosquito in 1898 and in 1900 Sambon and Low showed that 
it was possible to remain immune from disease in the most malarious 
region of the Roman Campagna if protected against mosquitoes 
while Dr. Manson’s son and another voiunteer were inoculated 
with malaria in England by the bites of infected mosquitoes shipped 
alive from Italy. 
The malaria germ is an example of a parasite which requires 
two different hosts in which to complete its life history. Asexual 
cycles are completed in the blood of man at regular intervals of 48 
or 72 hours, the recurrent period of chill and fever corresponding to 
the time at which new generations are set free in the blood stream. 
The complete development of the parasite, however, must be accom- 
plished in the stomach of a mosquito belonging to the genus A nopheles. 
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