MOSQUITO PROPHYLAXIS. 
By E. P. Mrnerv, M.D., D.P.H., D.T.M. & H. 
First I ask your pardon for a digression from the title of this paper to briefly 
review the mosquito itself and its relation to disease. 
Mosquitoes belong to the tribe of Culicidae or gnats, and as you are well 
aware if you reside for any length of time in Georgetown, they bite, hard and 
often. 
THE CYCLE OF EXISTENCE. 
Their cycle of existence is briefly as follows: The female lays the eggs 
in water, usually anything from 20 to 200 in number, in small rafts ; 
these hatch out in about 48 hours, under suitable conditions, into the 
larve stage known as “‘ wrigglers.” These must live in water, if they 
are dried they die. They are extremely active and almost uncanny in 
their intelligence, for example, on approaching a tub of water contain- 
ing larve, as soon as a shadow passes over the surface they all immediately 
wriggle off to the bottom and lie quite quiet. They never expose them- 
selves against anything white, but keep to the dark background where 
they are invisible. These “ wrigglers ’ in about a week change into the 
next stage known as the “pupa” or chrysalis stage; these are rounded 
bodies, very active, which also live in water. Both larve and pupe 
come to the surface frequently to breathe, the larve by means of 
a tube in the tail called a ‘“ siphon tube,” and the pupe by means 
of two ear-like projections at the side of the head. It is absolutely 
necessary for them to come to the surface frequently, or they die— 
are in fact drowned. Observers have calculated that five mnutes is 
the longest time a larva can remain under water at a stretch. This 
is incorrect, however, they can stand several hours total immersion. 
The pupa lives for one or two days, then it floats to the surface of 
the water, the covering is ruptured on its upper surface, and the adult 
mosquito, the ‘‘imago,”’ emerges. But it is not yet able to fly, it uses 
the old pupa skin as a boat, and floats about in it until it has had 
time to smooth out its wings and dry them in the sun, then it can 
fly away to become one of the greatest curses known to mankind 
carrying sickness and death in its track wherever it goes, 
The adult mosquito does not live for one day only, as many people imagine, 
it may live for months, and has been kept alive in glass tubes experimentally 
for as long as ten weeks. Some varieties can even hibernate in countries 
like Italy. The adult females only suck blood feeding on birds and animals 
as well as on man; the male is comparatively harmless and in most cases lives 
on fruit only as owing to his long bushy “ whiskers” or antenne, he finds it 
very difficult to bite animals. 
