﻿IX, B, 5 Walker and Barber: Malaria in the Philippines 435 



tertian and quartan malaria is insufficient to determine the 

 fact, it is probable that this species is also an efficient carrier 

 of these types of the disease. This species is from three to 

 four times as susceptible as Anopheles rossii, which has hitherto 

 been considered the malaria carrier of the Philippines, and 

 eleven times as susceptible as Anopheles barbirostris. 



The number of mosquitoes of the species Anopheles sinensis 

 and Anopheles maculatus dissected, especially in the compar- 

 ative experiments, is too small to give reliable percentages. It 

 is possible that a larger series of experiments with Anopheles 

 sinensis would show that this species can be infected. Its 

 susceptibility, however, is probably feeble. We believe it to be 

 the least susceptible of the five species with which we experi- 

 mented. The percentage, 66.66, of infections of Anopheles macu- 

 latus in the comparative experiments was obtained with only 3 

 specimens, and is probably too high; that of 6.12 in the total ex- 

 periments is probably too low. We are of the opinion that the 

 susceptibility of this species is at least as high as that of Ano- 

 pheles rossii, and probably lies between that of the latter species 

 and that of Anopheles febrifer. 



The role played by a species of Anopheles in the transmission 

 of malaria in any country depends chiefly upon (1) its suscep- 

 tibility and (2) its geographical distribution and prevalence; 

 also, to some extent, upon (3) its avidity for human blood and 

 (4) its domesticity. 



Of these factors susceptibility is of fundamental importance. 

 It is obvious that a mosquito which is immune or only slightly 

 susceptible to infection with the malarial parasite will, no matter 

 how prevalent or widely distributed, be of little or no importance 

 in the transmission of malaria; on the other hand, a very sus- 

 ceptible species may, although less prevalent, play a leading 

 role in the spread of this disease. For example, Anopheles 

 rossii was collected in native houses in certain regions in India 

 by Stephens and Christophers and others in far larger numbers 

 than was Anopheles culicifacies ; but, while the latter species 

 was found naturally infected with malarial parasites to the 

 extent of from 4 to 16 per cent, not a single Anopheles rossii was 

 found infected. These authors, therefore, concluded that Ano- 

 pheles rossii, although more prevalent, played a subordinate, 

 while the less plentiful Anopheles culicifacies played the chief, 

 role in the transmission of malaria in these regions. 



A species that was rare or limited to certain regions or alti- 

 tudes might, although very susceptible, be of little importance 

 in the dissemination of malaria in a country as a whole. A 



