SCREENING 197 



screened houses in the United States are perfectly screened. I 

 will say this, that I saw not a single cantonment that was even 

 well screened. " 



ESSENTIALS OF GOOD SCREENING 



The first consideration in good screening is to apply it only to 

 houses in a state of repair that justifies screening. Therefore, 

 in starting a screening campaign, the houses should be carefully 

 inspected and divided into three classes: (1) Those already in a 

 satisfactory condition; (2) those that can be put in such condition; 

 and (3) those that cannot be successfully screened. The last 

 class should not be touched, and the second should not be touched 

 cither, until the necessary repairs are made. 



A No. 16 mesh cloth is sufficient for Anopheles mosquitoes, 

 but, if protection against all mosquitoes is desired, the cloth 

 should be at least 18 meshes to the inch, as Aedes calopus can 

 pass through a No. 16 mesh. Varying conditions may demand 

 the use of different kinds of screening material, but, for adequate 

 protection against all mosquitoes, nothing less than 18 meshes 

 to the inch should be considered, or, if a screening material of 

 less than this be used, it should be painted. 



A third essential is that the work be carefully done. This 

 means that certain rules, evolved by experience, should be 

 followed, and that the work should be executed with skill and 

 care. 



A fourth essential is that no opportunity for tampering with 

 the screening be afforded. This means that no easily removable 

 screens be used. As already pointed out, if screens of such type 

 are employed, they will be sure to be left open occasionally. 



Finally, every opening in the house should be screened. It 

 will not do much good to screen the doors and windows, if the 

 chimneys are left unprotected and open spaces are left elsewhere. 



SCREENING OF DOORS 



Since screening, like the proverbial chain, is only as effective 

 as its weakest point, especial attention should be paid to this 

 weak point, which, in most cases, is the door. This is because it 

 is the one movable section most frequently used and, therefore, 

 is most subject to the carelessness of the people who use it. 



As mosquitoes are prone to congregate on the sheltered or 

 leeward side of a building, rather than on the windward side, it is 



