426 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 15 



of the individual experiments was changed daily. The duration of each 

 series of experiments varied from 5 to 11 hours ; in nearly every instance 

 it covered the time from 11a.m., till 4 p. m., when flies were most abun- 

 dant and active. During showers the receptacles were covered. 



Flies were always present but never abundant in this location; 17 

 was the largest niunber counted at any time. For this reason, a small 

 number of experiments was run almost daily throughout the period 

 covered by this investigation rather than a large number for a short 

 period of time. 



The bran employed was a sterilized commercial product, especially 

 prepared for culinary purposes. It consisted largely of wheat husk. 

 Except in a few instances, it was not sterilized before use. All chemicals 

 were of C. P. grade. Well water was used in all solutions and for other 

 purposes where water was required. 



The carbcn dioxide used in these experiments was liberated from 

 sodium carbonate by means of sulfuric acid. The acid (specific gravity 

 1.84) was diluted to 20 percent, by voltmie before use. A generator 

 consisting of a 400cc. salt -mouth bottle or a milk bottle of pint or quart 

 capacity equipped with a dropping funnel and a glass delivery tube 

 supplied the gas which was conducted through a rubber tube to the 

 experimental receptacle. Forty, 50 or 100 g. of sodium carbonate in 

 30 to 60cc. water were decomposed by the slow dropwise addition of the 

 dilute acid. The flow was regulated to give a steady evolution of carbon 

 dioxide from 11a. m., till 4 p. m., or longer. The bran nidus was ex- 

 posed in the glass funnels or porcelain dishes mentioned above. The 

 funnels were 10.2 cm. in diameter; each held a perforated procelain 

 disk 5 cm. in diameter which prevented the bran from clogging the stem 

 of the funnel. Each funnel contained about 15 g. bran (air dry weight) 

 well moistened just before the experiment started. The generator 

 tube was attached to the stem of the funnel and in this way carbon 

 dioxide was conveyed through the bran and into the air above. The 

 porcelain dishes measured 13.3 cm. in diameter and 2.5 cm. in depth. 

 A piece of absorbent cotton occupied the bottom of each dish to help 

 retain miosture; over this the bran was spread and the glass nozzle 

 of the generator tube was thrust in the center of the bran mass. Water 

 was added to each dish. Further details concerning the carbon dioxide 

 dish experiments are given in table I. 



Porcelain dishes were generally used for the ammonium carbonate 

 experiments. Each dish contained a piece of cotton, 10 g. bran (in 

 one case 20 g.) and 25 to 30 g. of solid ammonium carbonate (an 

 equimolecular mixture of ammonium bicarbonate and ammonium 



