16 



The Philippine Jownal of Science 



1918 



taken blood and separated after the first feeding gave 27.7 per 

 cent positives. Of those not separated, but as a rule given 

 repeated feedings, 451 dissections gave 26.6 per cent positive, 

 a percentage little below that of those known to have taken 

 blood. 



It may be of interest to know what relation, if any, the 

 number of times mosquitoes exposed to gamete carriers bears 

 to the percentage infected and to the average number of oocysts 

 per positive mid-gut. 



Crescent series alone give the best basis for comparison, and 

 such dissections, all from the controlled series, are summarized 

 in Table VII. 



Table VII. — Relation of the percentage infected and the average nu?nber 

 of oocysts per mid-gut to the number of times exposed to a crescent 

 carrier. 



Exposed to carrier. 



Dis- 

 sected. 



Positive. 



Average 

 oocysts 

 per mid- 

 gut. 



Once 



415 

 213 

 208 

 102 

 20 

 18 



Per cent. 

 20.5 

 27.2 

 18.8 

 30.4 

 45.0 

 72.2 



9.9 

 12.4 

 21.3 

 4.3 

 8.9 

 3.2 



Twice.. . — 











Total _ 



976 



24.1 



11.3 





Twelve species with greatly varying susceptibility to infection 

 are included in this summary, and the probable error is great; 

 however, the numbers are large enough to indicate that there is 

 no very marked positive correlation of number of feedings to 

 percentage infected or average number of oocysts, except that in 

 the aggregate those exposed four, five, and six times show a 

 higher percentage of infections than those exposed fewer times. 



There was little indication in any series of infection exper- 

 iments of a new infection occurring in a once infected gut through 

 a later feeding of the mosquito on a carrier. There was some 

 variation in the size of oocysts, but such variation could be 

 found in insects exposed but once. Further we note in Table VII 

 that the average number of oocysts does not increase with the 

 number of feedings. The most probable case of a superimposed 

 infection was afforded by a lot of umbrosus collected in the adult 

 stage. These showed a fair percentage of specimens infected 

 previous to exposure to a gamete carrier. A lot of these were 



