1915] Behavior of Anopheles 249 
bottom where they remained almost motionless. None came 
to the surface until thirty minutes after the stream was cut 
off. Chlorine and bromine gases had very decided effects; 
immediately the gas was introduced the larve began to wriggle 
violently, and after the first minute slowly lost all motion. 
Some remained at the surface, others at the bottom. Five 
minutes of either gas was sufficient to kill all larve at the 
end of one hour and ten minutes exposure in the water. 
Successful introduction of a gas into water breeding mos- 
quitos would kill all larve in short time and.would prove a 
valuable agent in the reduction of breeding. But from the fact 
that the average native is not over-careful as to the kind of 
water he drinks, extreme caution must be used in the gas 
used. Under certain conditions it would be quite effective to 
introduce suitable electrodes into saline waters breeding 
mosquitos and destroy these by the liberation of chlorine gas 
through electrolysis. 
2. The Adult Stage: Elsewhere it had been stated that the 
food of the female Anopheles transmitting malaria is probably 
restricted to human blood and that this exclusive diet was 
reached by a gradual adaptation and restriction to the human 
race, covering probably centuries of time, and probably at some 
period thereof has been accelerated by the introduction and 
establishment of the malarial parasite. That such mosquitos 
are restricting themselves to inhabited regions is clearly in 
evidence on the Canal Zone. Regions away from habitations 
have habitats which are identical in every respect to those on 
the Zone which breed albimanus, and yet they are sterile 
as to such species. Nor are there adults of such species in the 
bush nearby. In the malarial mosquitos this restricted adaptation 
is not as complete as that of the yellow-fever mosquito, Aedes 
calopus Meigen, but an unmistakable trend in the direction 
of greater restriction is plainly in evidence. Females pre- 
dominate by great percentage in all traps attached to buildings 
and in mosquitos caught inside of buildings. The proportion 
is as high as 250 : 1. Smears of the stomach contents of over 
a hundred males caught in Gatun barracks showed no case 
of a human blood meal. It is also quite probable that if males 
did suck human blood, some member of the sanitary corps would 
have noticed instances of it. It seems that the male Anopheles 
