138 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 



At the beginning of the work, with so gigantic a task to perform in 

 the shortest possible time, the most energetic efforts were necessary 

 and measures were adopted that would produce the most immediate, 

 although temporary, results. When the situation, however, was 

 somewhat in hand, the practice was modified and work of a more 

 thorough and permanent character undertaken. The principle under- 

 lying mosquito control as now practiced in the Canal Zone is the grad- 

 ual creation of permanent conditions inimical to mosquito propagation, 

 while the situation is kept in hand by more or less superficial and 

 temporary work. Prophylaxis is practiced in the careful screening of 

 quarters and the administration of quinine, as universally as possible, 

 to those exposed to infection. 



The attainment of the ideal condition of a permanently mosquito- 

 free territory through artificial means is manifestly impossible in such 

 a climate as that of Panama. The battle with nature is unending and 

 the slightest relaxation means a rapid reversion. Yet work of a 

 permanent nature is, in the end, far more economical and leaves the 

 sanitary forces free to carry on the fight upon the outlying portion of 

 the controlled area, gradually forcing back the danger line and extend- 

 ing the zone of permanent improvement. By permanent work is 

 meant primarily the thorough and rapid drainage of the land, either by 

 the use of tile or by open concreted ditches, the drainage of permanent 

 swamps and the filling in of low ground. Open ditches through earth 

 or clay are exposed to rapid deterioration and require constant care, 

 with attendant expense and lower efficiency. 



Among the important phases of permanent or semipermanent work 

 is the clearing away of the bush or jungle which would give shelter to 

 mosquitoes in the vicinity of habitations. The area cleared varies 

 with the conditions, but usually a belt approximately iOOO feet 

 wide about inhabited buildings is desired. The cutting of grass in the 

 same situations should be included with the work just mentioned, 

 though this must be performed sometimes as often as once each month. 



As a supplement to permanent or temporary drainage, the means 

 on which most reliance is placed is the use of larvacides, either in the 

 shape of crude oil or a combination of caustic soda, crude carbolic 

 acid and resin, which is manufactured by the Department of Sanitation. 

 Each of these materials has its faults and advantages. The oil is 

 bulky and drifts with the wind to one end or another of the body of 

 water, leaving a large part of the surface exposed to oviposition. 

 When "cut" with about ten per cent, of the "larvacide," by which 

 broad term the manufactured product is designated, it is largely used 

 on small collections of water, such as hoof-prints, where the surface 

 can be entirely covered and, unless floated out by inundation of the 



