30 The Control of Mosquitoes 



is from seventy to eighty inches per year. Toward 

 the divide the rainfall increases, and between 

 Culebra and Colon is very heavy, increasing as the 

 Atlantic coast is approached. The annual precip- 

 itation at Colon is between 120 and 180 inches. 



The country along the line of the Canal is low 

 and near tide level for a distance of six miles from 

 the Pacific, and fifteen from the Atlantic ocean. 

 The remainder of the country is thickly studded 

 with hills and contains numerous springs, seepage 

 outcrops, swamps, and streams. The Canal ap- 

 proximately follows the line of the Chagres River as 

 far as the divide at Culebra Cut, and then down 

 the valley of the Rio Grande to the Pacific. There 

 is very Httle porous soil on the Isthmus, and a large 

 part of the surface soil is of a claylike character 

 and is so densely clothed with luxuriant vegetation 

 that travel is impossible except along the trails, 

 which if not constantly used soon become over- 

 grown and disappear. The lands immediately 

 adjacent to the Canal produce more mosquitoes 

 than places a mile or more east and west of it. 

 There are extensive areas toward the Canal Zone 

 boundary line and in the Republic of Panama 

 in which Anopheles do not exist. 



The meteorological tables, on the pages pre- 

 viously referred to, show the large percentage of 



