DDT Formulations 73 



observation and lighting, and various openings for admitting 

 insects and insecticide, and for ventilation after the test. 



After the flies are in place, 12 milliliters (about % 02.) 

 of the insecticide are injected into the chamber with a special- 

 type atomizer. Ten mi nutes later, the ventilating fan is 

 turned on, the door is then opened, and the number of flies 

 clinging to the ceiling and walls, together with any that are 

 still flying, are counted. These are considered to be unaf- 

 fected by the inseaicide. The flies which have fallen to the 

 floor are transferred to observation cages and are examined 

 at the end of 24 hours to determine the number which are 

 dead. Any flies that have revived during this period are also 

 considered as unaffeaed by the inseaicide. The percentage 

 of the original flies which are found dead at the end of 24 

 hours is known as the percentage kill. 



Each time an insecticide is tested, duplicate runs are 

 made — one with the insecticide being tested and the other 

 with the official test insecticide of the National Association 

 of Insecticide and Disinfectant Manufacturers, Inc. If the in- 

 secticide being tested has a "kill" of from 5 % less to 5 % 

 more than that of the official test insecticide, it is given the 

 designation Grade B. If its "kill" is from 6 to 15 % great- J 

 er, it is classified as Grade A. And if its "kill" is 16% or jf 

 more above that of the standard, it carries the highest rat ing p 

 of all — Grade AA. 



Now you know what the words Grade AA on an in- 

 seaicide label mean. But, you won't find the letters AA, 

 A, or even B on all household sprays. This does not neces- 

 sarily mean that the insecticide is of poor quality, for you 

 must remember that acceptance of Commercial Standard 

 CS72-38 is not compulsory, and some manufacturers just 

 haven't bothered with it. However, most inseaicide manu- 



