66 



easily separated from those wkich were not and also from the males. 

 Attempts to induce the insects to feed in the day-time were very 

 rarely successful. The gorged mosquitos were killed with chloroform 

 and dissected; 184 experiments were made and minute details are 

 given of the results. There would seem to be no difficulty in rearing 

 insects from larvae in the laboratory. The percentage of females 

 was as follows : — A. minimus {febrifer) 53-8, A. rossii, 57-6>4- harhi- 

 rostris, 58-3, A. sinensis, 59-8, and A. ?naculatus, 400. There is thus a 

 slight preponderance of females, except in the last case, in which the 

 numbers used hardly justify a conclusion. The percentage of females 

 that lived to be dissected was, in the same order as above, 55-0, 42"2, 

 61-9, 78-2, 1000. The avidity for human blood, i.e., percentage of 

 those that fed was, again in the same order, 54*8, 63-6, 49-4, 67-8, 500. 

 A table is given showing the number of gametes in the blood and the 

 percentage and intensity of infection of the mosquitos. The highest 

 infection was obtained when the gametes in the blood were between 

 15-20 per cent, of the leucocytes, and the percentage of infected 

 mosquitos, when this ratio was between 80 and 90 per cent., fell to 

 4-5 from 40 9 with a gamete percentage of 75-80. From this table, 

 it is apparent that, given a malarial patient whose blood contains 

 gametes above the limits of infectiousness, the percentage of infections 

 and the intensity of infections do not depend alone Upon the nimaber 

 of gametes ingested, but that some other factors must be involved 

 in their determination. The percentage of each species infected, the 

 nature of the infection, and other material details are carefully set 

 out in tables. The role played by a species of Anopheles in the trans- 

 mission of malaria in any country is stated to depend chiefly upon 

 (1) its susceptibility 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 impor- 

 tance. 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 susceptible 

 species may, although less prevalent, play a leading role in the spread 

 of this disease. For example, A. rossii was collected in native houses 

 in certain regions in India by Stephens, Christopher and others, in 

 far larger numbers than was A. 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 A. rossii was found infected. These 

 authors, therefore, concluded that A. rossii, although more prevalent, 

 played a subordinate, while the less plentiful A. culicifacies played the 

 chief role in the transmission of malaria in these regions. The 

 distribution and relative prevalence of the Philippine Anophelines is 

 now being studied, but the importance of the 5 species now investigated, 

 in the transmission of malaria in the Philippines can be roughly 

 estimated as follows : — 



A. maculat'us, moderately susceptible to infection ; semi- wild ; avidity 

 for human blood moderate ; distribution very local ; not an important 

 carrier. 



A. sinensis, low or negative susceptibilit}'' ; wild; avidity for blood 

 high ; scarce and probably negligible as a carrier. 



