90 The Control of Mosquitoes 



shining. Although so many were under the houses 

 none came out to bite anyone standing in the sun. 



The Gatun salt-water swamp was the source of 

 these mosquitoes.^ The houses affected were 

 numbers 3, 184, 185, 195, and 220, located near the 

 railroad depot. ^ There are many other houses 

 at Gatun, some less and some equally distant from 

 the propagation area. Under most of them no 

 mosquitoes were present in the daytime. 



Although it is customary for mosquitoes to bite 

 soon after sunset, cases have been known where 

 observers remaining in one place from six p.m. were 

 not bitten until eleven p.m., when Anopheles 

 alhimanus became suddenly numerous and fed 

 freely. When the jungle surrounding houses was 

 cleared, for several days mosquitoes entered them 

 in much larger numbers than before the clearing 

 was made. It is said that a fairly brisk wind 

 prevents the flight and biting of mosquitoes, but 

 on the Atlantic slope where the trade winds blow 

 nearly aU the year round, they often bite at dusk 

 whether the wind blows or not. In infested settle- 

 ments mosquitoes are seldom found in vacant 

 houses. 



When houses are imperfectly screened Anopheles 

 are more apt to find defects than other mos- 



' See map p. loi. » See map p. loi. 



