Screening and Destruction 199 



Canal Zone must have not less than ninety per 

 cent, of pure copper, and not more than one half 

 of one per cent, of iron. The cost of this screening 

 is approximately fifty cents per square yard for the 

 18 mesh, No. 31, B. W. G. gauze, i.e., gauze having 

 eighteen strands of wire of one one htindredth 

 of an inch diameter in each Unear inch, which 

 is the number of strands necessary to reduce the 

 apertures to a size that will not permit the passage 

 of A'edes calopus and the smaller specimens of 

 Anopheles and Culex, and yet retain reasonable 

 strength of material and open space area. 



Verandas are usually screened as shown on the 

 photograph. In the tropics the veranda is practi- 

 cally the living room; people usually spend their 

 evenings in it, and it must be screened. Aside 

 from the fact that screened verandas contribute 

 very largely to the comfort and probably to the 

 health of the occupants 'of the dwellings, screening 

 on verandas is easier and cheaper to maintain than 

 the screening of many doors and windows that 

 would otherwise have to be screened. And 

 because of their larger air and light admitting 

 area, screened verandas do not exclude quite as 

 much air and light as screened doors and windows. 



A decided advantage is gained by having but 

 one door through which mosquitoes may enter. 



