Pathogenesis 



487 



begin to fly at dusk, the patients should shut themselves in before 

 that time. By thus killing the parasites in the blood, and keeping 

 the mosquitoes from the patients in the meantime, much can be done. 

 But where malarial fever prevails, the mosquitoes are already largely 

 infected, hence the healthy population should also learn to respect 

 the habits of the insects and not expose themselves to their bites, 

 should screen their houses and their beds, and should take small 

 prophylactic doses of quinin to prevent the development of the 

 parasites when exposure cannot be avoided. 



2. The Mosquitoes. — ^It is not known that the parasites can 

 pass from one generation of mosquitoes to another, hence the 

 mosquitoes to be feared are those that are already infected. By 



Fig. igo. — Anopheles maculipeimis : Adult male at left, female at right (Howard). 



making the houses mosquito-proof most of the insects can be kept 

 out, while those that get in can be caught and killed. 



By draining the swamps and destroying all the breeding places 

 in and near human habitations, the number of mosquitoes can be 

 greatly diminished. Fortunately this is particularly true with 

 reference to the mosquitoes most concerned — the anopheles — which 

 fly but short distances. By closing all the domestic cisterns and 

 reservoirs, cesspools, etc., so that no mosquitoes can get in to breed 

 or get out to bite, and by draining the pools for half a mile in all 

 directions from human habitations, the number of anopheles mos- 

 quitoes can be made almost negligible. If at the same time no 

 mosquitoes are any longer permitted to infect themselves by biting 

 infected human beings, the spread of the disease must be greatly 

 restricted or checked. 



