462 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 14 



trying one attractant against another. The results on different sub- 

 stances should therefore be directly comparable with one another. 

 In regard to strength of solutions of the different substances used, 

 it should be stated that with the exception of sodium carbonate, sodium 

 sulphate, and calcium hydroxid, thej^ were made of approximately equal 

 chemical strength; that is, the potential hydrogen ion or equivalent 

 was the same in all cases, and equal to that in a 2 percent (by weight) 

 solution of butyric acid. The two salt solutions, sodium carbonate 

 and sodium sulphate were of the same molecular concentration as the 

 butyric acid; that is, double the potential ionic strength. The calcium 

 hydroxid solution was saturated at 20 C. The amount applied to each 

 unit of nidus was from 2 to 4 cubic centimeters. Since the experimental 

 work started with but^Tic acid, and when it was found that from 2 to 4 

 cubic centimeters of a 2 per cent solution of this attractant seemed 

 most effective, additional substances were made up and applied on this 

 basis. 



In this way it has been possible to test out in a satisfactory^ manner 

 13 different substances in addition to carbon dioxid and ammonia; 

 and it is believed that the results in these cases fairly express the ovi- 

 position responses of the house fly toward the substances used. 



The Results of the 88 experiments made in the two seasons are sum- 

 marized in Table I. 



Table I. Oviposition Response of the House Fly to Certain Chemicals 



1918 



