PROPHYLAXIS OP MALARIA. 
43 
hours. In practice it has been found that even in the worst malarial 
regions a surprisingly small percentage of mosquitoes examined are 
found infected, if one considers the actual number of infected indi¬ 
viduals present and the apparent chance of infection of the mosquito. 
In Italy Celli found only 2.5 per cent of the Anopheles examined 
by himself infected; A. Plehn, in Africa, examined 860 Anopheles 
and found 2.2 per cent infected; La Monaco found about 5 per cent 
infected; and the Sergents, in Algiers, found 1.6 per cent infected. 
At Camp Stotsenburg, in the Philippine Islands, the percentage of 
naturally infected mosquitoes varied greatly, being as high as 35 
per cent during the height of the malarial season and ns low as 1 
per cent at other times. 
The species of mosquito in relation to the transmission of ma¬ 
laria. —It is now a well-established fact that certain of the Anoplie- 
lince do not transmit malaria and can not be infected experimentally. 
The observations of Stephens and Christophers in India showed 
that while 12 of 259 Myzomyia culicifacfes dissected by them shown 
infection with malarial sporozoites , not a single one of 496 Myzomyia 
rossii showed infection, while Hirshberg found that out of 58 Ano¬ 
pheles punctipennis experimentally none developed an infection, 
while of 48 Anopheles maculipennis 8 became infected. In the Canal 
Zone Darling 8 found that, in his experiments, 70.2 per cent of 
Cellia ( Anopheles ) albimctnus became infected; 60 per cent of Ano¬ 
pheles tarsimaculata , and 12.9 per cent of Anopheles pseudopuncti- 
pennis. On the other hand, he found it impossible to infect Anopheles 
malefactor , which, as he says, despite its name, is not a factor in the 
transmission of malaria in the Canal Zone. 
From these observations it is evident that even though anophelines 
may be present in a locality, it does not follow that malaria is present 
or that the disease could spread if it were introduced. In other 
words, the right species of Anopheles must be present in order to 
transmit the infection, and hence it follows that the determination 
of the species present in any locality becomes an important pro¬ 
phylactic measure. 
Not only are some of the Anophelince unable to act as hosts of the 
malaria plasmodia but some species can only act as host for a 
certain species of plasmodium, so that the prevalence of the dif¬ 
ferent types of malaria in any locality depends upon the species 
of mosquito present. Beyer, Pothier, Couret, and Leman 9 have 
shown that while Anopheles quadrimaculatus became infected ex¬ 
perimentally with the tertian and quartan plasmodia it was impos¬ 
sible to infect it with the aestivo-autumnal plasmodium, while, on 
the other hand, Anopheles crucians was shown to be a host to the 
aestivo-autumnal plasmodium but could not be infected with the 
tertian or quartan plasmodia. Kinosliita 10 found that Anopheles 
