50 
PROPHYLAXIS OF MALARIA. 
biting occurred during the middle of the day, in the sunlight, but 
prophylactic measures based upon the twilight habit would prevent 
the vast majority of bites. 
Flying distance .—In most of the older publications dealing with 
mosquitoes it is stated that they do not cover great distances in flight. 
This statement, in the light of our modern researches, can no longer 
be considered correct, even in regard to the Anophelince . In 1900 18 ,1 
published a statement that from personal observations I believed that 
certain species of Anopheles often flew from 2 to 24 miles in order 
to reach the post where the observations were made, and this state¬ 
ment, being so much at variance with generally received opinions 
regarding the flight of anophelines, was subjected to much criticism 
by entomologists. Since then my observations have been confirmed 
by workers upon the Canal Zone and by James and Christophers in 
India 19 , as well as others, and it is now well recognized that while 
anophelines prefer to breed near their prey, they will fly long dis¬ 
tances in order to lay their eggs or to feed, provided there are no 
breeding places in the near vicinity. 
The experiments of the department of sanitation in the Canal Zone 
in regard to the flight of anophelines are of special interest and value. 
In their report they say 20 : 
Adult anopheles were stained with dye and liberated at the swamp. Subse¬ 
quently some of them were collected on the opposite side of the river, at the 
locks, and in houses 4,700 feet from the liberating station. It should be stated 
that the anopheles’ flight was decidedly marked and was easily noted by half a 
dozen witnesses, when their attention had been drawn to it. Even so, not one 
person in areas thickly infested did note the flight until shown the way to ob¬ 
serve it. 
Regarding the flight of the anopheles the report states: 
The flight was from west to east and quite marked. As it became darker the 
quantity of flying anopheles increased, and by looking at a dark object against a 
clear sky hundred of anopheles could be seen passing by. 
The mosquitoes flew from the propagation area in a swamp to 
Gatun, and some of the breeding places were more than 2 miles from 
Gatun. 
At Mian Mir, James found adult mosquitoes present when no 
larvae could be found within 2 and 2J miles, and Le Prince 21 deter¬ 
mined that Cellia ( Anopheles) alhimanus , the principal transmitter 
of malaria in the Canal Zone, will travel against a 4-mile breeze for 
distances of a mile, and possibly farther. 
The confusion regarding the distance of flight of anophelines is 
undoubtedly partly due to observers studying different species, but 
while it is probably true that the majority prefer to fly short distances 
in order to reach their food, it must be recognized that these mos- 
■ . ••••'• - • ...JOi. 
quitoes are capable of flying for two or more miles, and this fact 
