The Campaign at Havana 9 



Finally, it was decided that the breeding place 

 must be local, and the labor force was put in line, 

 men eight feet apart so that every square yard of 

 the hill would be seen, and no wet place, however 

 small, could be missed. They marched along for 

 some time before a piece of partially soft ground 

 was found. There were no surface indications, 

 such as a change in the vegetation or its color, 

 to mark the outline of the wet area. A thin film of 

 water was found to outcrop along a contour line, 

 to run along the surface for a distance of about 

 twenty feet, and then disappear into the ground. 

 The mosquito larvs were very plentiful. A ditch 

 was made above the seepage outcrop line, but 

 failed to intercept the water. Two short and deep 

 parallel intercepting ditches were made about nine 

 feet apart, but failed to prevent the water coming 

 up between the two ditches. It became evident 

 that the local porous water-bearing strata were 

 inclined and pointed upwards, and that a distant 

 pressure was forcing the water uphill. Ditching 

 was out of the question. At a small cost the 

 ground affected by the surface flow was covered 

 with gravel and cinders to a depth of about six 

 inches, so that the mosquitoes could not reach the 

 water which continued in its original path. 



Since that time the importance of hidden mos- 



