100 The Control of Mosquitoes 



The daily inspection was supplemented by night 

 observations ; the shore and the lake just off shore 

 being observed. No mosquitoes were present on 

 the lake at night and people in small boats close 

 to the lake shore not far from the settlement were 

 not bitten. It was evident after making many 

 observations that the lake was not the source. 

 Careful examination of all the territory to the 

 north of the settlement failed to show any breeding 

 places of sufficient extent or importance to account 

 for the influx. The area to the west was examined 

 last, because of the extensive cleared area west of 

 the settlement which was known to be free from 

 possible breeding places. ^ 



To the west of the old French canal there was 

 some flat land into which the sea water and mud 

 from the American canal was being pumped. This 

 place had never before produced mosquitoes that 

 affected Gatun, and was so located that to reach 

 the settlement the adults would have to fly from 

 half a mile to a mile straight across or at right 

 angles to the stiff breezes which prevail at Gatun in 

 the dry season, over ground containing very little 

 protection from wind by high grass or bushes. 

 Flight of this length under such conditions was 

 not thought to be possible. Between the wet area 



' See map. 



