﻿IX. B, 5 Walker and Barber: Malaria in the Philippines 383 



was taken advantage of, if the mosquito did suck blood whether 

 or not the blood contained gametes sufficiently numerous to 

 infect the mosquito, and whether or not sufficient time had 

 elapsed after the feeding for the parasites to attain develop- 

 ment. In properly conducted experimental infections all of 

 these essential factors are under complete control. We are 

 also of the opinion that it is strong, if not wholly sufficient, 

 proof of the capacity of a species of mosquito to transmit mala- 

 ria if it can be infected with the malarial parasite and if the 

 parasites develop sporozoites and infect the salivary glands, 

 without subjecting healthy persons to the bites of the experimen- 

 tally infected mosquitoes. It is improbable, although possible, 

 that sporozoites should be developed, migrate to and infect the 

 salivary gland of the mosquito, and yet be incapable of being 

 injected into or of infecting man. As it is known that different 

 species vary greatly in their ability to transmit malaria, it is 

 of the greatest practical importance to determine the relative 

 susceptibility of the different anophelines in any country. In 

 most infection experiments hitherto performed, careful com- 

 parative tests have not been made to determine the relative 

 susceptibility of the different species of anophelines. In some 

 cases a rough estimation of the proportion of a given species 

 that becomes infected has been obtained. However, to be of 

 practical value, the test should be comparative of different spe- 

 cies of anophelines in a given region. This can be accurately 

 determined only by a large series of experiments in which the 

 different species are fed at the same time upon the same mala- 

 ria patients and in which only those mosquitoes that sucked a 

 full meal of the infected blood are selected for dissection. 

 Under these conditions of experimentation the percentages of 

 infected mosquitoes, and the relative number of oocysts in the 

 infected individual of the several species, will give a reliable 

 index of the relative susceptibility of these anophelines to 

 infection with the malarial parasite. 



Susceptibility, while the most important, is not the only factor 

 in determining the importance of any species of mosquito in the 

 transmission of malaria. Geographical distribution and preva- 

 lence of the species, its habitat in relation to the dwellings of 

 man, and its avidity for human blood also play a more or less 

 important part in determining the role of the different species. 

 All of these factors must be determined for each species before 

 we can estimate accurately their relative importance in the 

 epidemiology of malaria in any country. 



In the Philippine Islands the species and distribution of the 



