December, '22] Richardson: house fly and carbon dioxide 429 



percent, ammonia. Porcelain dishes containing cotton, 10 g. bran 

 and 50 cc. of the ammonium hydroxide solution were usually employed. 

 On July 31,8 eggs were found in a dish to which 50cc. of a solution con- 

 taining 2 percent, ammonia had been added, and on August 5, 390 

 eggs were counted in a dish which held the same amount of a solution 

 containing 14 percent, ammonia. Time did not permit a more thorough 

 investigation of this subject, but we hope to return to it in the future. 

 The partial success with ammonia noted here and in previous experi- 

 ments\2 together with the negative results obtained with carbon dioxide 

 again lead to the conclusion that the female house-fly is attracted 

 largely by the odor of ammonia. 



Aqueous solutions of ammonium carbonate and ammonium hydroxide 

 differ in a ntimber of partict^lars which may account for this difference 

 in attraction. With solutions of equal percentage concentration of 

 ammonia, ammoniimi carbonate solution evolves ammonia much more 

 evenly than a solution of ammonium hydroxide. An ammonium hy- 

 droxide solution gives off a large part of its ammonia during the first 

 2 or 3 hours of exposure, while an ammonium carbonate solution evolves 

 about one-third as much. The ammoniimi hydroxide solution will 

 also have a higher concentration of hydroxyl ion. These and other 

 differences may account for the greater attraction of an ammonitim 

 carbonate solution. 



The results described by Cnmib and Lyon represent, we believe, 

 the anomalous responses of house-flies reacting in an unnatural en- 

 vironment. 



It may be of interest to state in passing that Stomoxys cakitrans L. 

 was seen almost daily in the vicinity of these experiments but never 

 alighted on the bran. It is apparently not attracted to the compounds 

 used in this investigation. 



Conclusions 



1. Bran which volatilizes carbon dioxide alone when exposed in the 

 natural environment of the house-fly will not induce oviposition. 



2. Bran which volatilizes the products of decomposition of ammo- 

 noitim carbonate in aqueous solution attracts the house-fly and induces 

 egg-laying. 



3. Since carbon dioxide and water, two of the final decomposition 

 products of ammonium carbonate, do not in themselves induce egg- 

 laying, it is believed that ammonia is largely responsible for the attrac- 

 tion to ammoniixm carbonate. 



4. The possibility of other substances exerting an augmenting in- 

 fluence on the attraction to ammonia is admitted, but no definite proof 

 of it was indicated in these experiments. 



