December, '21.] crumb & lyon: chemicals and house fly 463 



Since the dosages are equal and the chemical concentration of the 

 different attractants is approximately the same, a better view of the 

 comparative effect may be obtained b}- eliminating the checks, and 

 listing the substances used with their corresponding percentages. Stated 

 in this fashion and listed in the order of diminishing attractiveness the 

 results appear as follows: 



Percent. 



1 . Sodium carbonate 94.2 



2. Carbon dioxid (carbonic acid)^ 92.4 



'■ . Acetic acid 83.8 



L Sodium hydroxide ^. , • 75.8 



•'). Butyric acid 73.5 



li. Sodium sulphate 69.6 



7 . Formic acid 66.7 



*^. Propionic acid 64.8 



It. Ethyl alcohol 58.5 



10. Glycerin 54.9 



1 1 . Lactic acid 46.3 



12. Hydrochloric acid 44.8 



13. Calcium hydroxide 42.8 



14. Sulphuric acid 37.5 



]."). Ammonia (ammonium hydroxid)' 32.6 



•Experiments carried on in 1917. 



