Anopheles Propagation Areas 77 



places where tall grass grew salt was not percepti- 

 ble to taste six hundred feet from the shore line. 

 In wading out from the shore the water was tasted 

 every few yards, and it was noted that young 

 Culex and Anopheles larvae appeared with the first 

 indication of brackishness. In going farther from 

 the shore as the water became more brackish the 

 Anopheles larvae found were more numerous and 

 more mature. When the water became salty 

 enough to be decidedly disagreeable to taste, 

 Anopheles larvae were most numerous. They 

 were more numerous per unit of area than had 

 been noted anywhere on the Isthmus during the 

 previous nine years of anti-mosquito work. The 

 absence of Anopheles and the scarcity of Culex 

 larvae in the wet zone not afEected by salt water was 

 unique. Tests made along shore at many points 

 established the fact. The condition was so 

 uniform that by wading slowly from shore to shore 

 with eyes closed, and testing by taste alone, we 

 were able to reach the infested zone and secure 

 larvas in collecting cups. The water surface 

 contained large quantities of leaves that had 

 fallen from the dying trees. Small larvae-destroy- 

 ing fish were quite numerous, but larvae of Anoph- 

 eles and Culex were so plentiful in the salty 

 water that it was impossible for the fish to make 



