HOUSE-FLY INVESTIGATIONS. 497 



Substances tested. Results. 



j^Qj.jjjj ( Did not poison house-flies or blow-flies. 



Boric acid ; ^^^^ "'^ difference in attractiveness of bait for house-flies, 



(. but were repellent to blow-flies. 



Picric acid C Made no difference in attractiveness for house-flies or 



(bait yellow) I blow-flies : both fed greedily upon it, and were appa- 



(. rently unharmed ! 



Amyl alcohol Strongly repellent to both house-flies and blow-flies. 



r Repellent to house-flies ; but after the smell had gone' off 

 Amyl acetate < *''® ^'^J*® "'^'"^ ^»^"^ attractive, and eggs were laid and 



I larvte lived in them. Flies were killed when it was poured 



L into trap containing them. 



Antimony oxide ^ ^'"^^ not kill house-flies, and made no difference in attractive- 



t "ess for them. 



Acetaldehyde Disliked by house-flies and blaw-flies. 



r Flies were killed when it was poured into trap containing 



Westoran < them. Next day no apparent difference seen in attrac- 



C tiveness of baits. 



Certain experiments were also made to test the poison-effect 

 of paraformaldehyde and formaldehj^de. 



Some typical results are given in the table on p. 498. 



It was not possible to arrive at any very definite conclusions 

 from the above experiments with formalin, as the results were so 

 varied. Sometimes the flies died after feeding on the mixtures, 

 while at other times they were apparently unharmed. Some 

 days they came in large numbers to feed, and on other days 

 few or none came. Generally speaking, more seemed to come 

 on tine than on dull days. One thing, however, seems clear, 

 which is, that if formalin is used in practice for ridding rooms 

 or buildings of flies, the " corpses " should be swept up and 

 burnt as soon as possible, so as to prevent any possibility of 

 recovery. 



It was, however, felt that further and more accurate experi- 

 ments should be made to test the poison-effect of formalin, etc., 

 on house-flies, where known quantities of formalin were added to 

 known amounts of bait. An account of these experiments is 

 given below. 



(ii.) Account of Exjieriments on Poison-hcdts when House-flies 

 ivere confined in cylinders. 



In order to secure more definite results than was possible 

 in the greenhouse, the following experiments were made at 

 the Imperial College of Science, in one of the laboratories, 

 having an ordinary roof with no skylights. Thither the 

 breeding-materials, maggots and pupee from the greenhouse, 

 were transferred. Very soon enormous numbers of flies had 

 emerged, which were used in the experiments. The supply 

 was kept up by breeding them in the same way as before. 



The substances to be tested, placed on pieces of glass, were fed 

 Proc. Zool. Soc— 1916, No. XXXV. 35 



