486 MISS O. C. LODGE ON THE 



11. Methods and account of ExjJeriments to find out lohen and 

 under tvhat conditions meaty substances are most attractive 

 to bloiv-flies. {June and Jtdy.) 



All these experiments took j^lace out of doors, the baits being 

 exposed in sunny places in the Zoological Gardens ; for it was 

 found that even when a very attractive bait was placed in. the 

 shade, pi'acticallj^ no blow-flies came to it, although they had 

 been swarming round it when it was put in the sun. 



The different substances were at first placed in shallow dishes, 

 partially covered by glass plates, so that the flies could enter and 

 feed, and the smell diffuse into the air. Later, however, it was 

 found more convenient to use glass pickle-jars (height 9 inches, 

 diameter 4 inches) fitted with wire-gauze funnels, which pievented 

 the flies from escaping when once they had gone inside. 



The number of flies caught in these jars was noted each 

 morning and evening, but when dishes were used they Avere kept 

 xmdei- as continuous observation as possible during the day, and 

 the attractiveness of the bait estimated by the number of flies 

 which had fed during that time. 



The average length of time of each experiment was from six 

 to seven days. 



The first substances to be tried were meat and hard-boiled egg, 

 of different ages. It was seen that after becoming blown their 

 atti-activeness was increased. This was especially the case when 

 they had been kept for a few days, and were in a more or less 

 liquid condition, owing to the digestive action of the maggots. 

 At this stage they were very attractive to the blow-flies, the 

 meat more than the Qgg, though numbers of flies came to both. 



This eflect of maggots on substances was further tested in 

 later experiments, when two similar pieces of meat were put out 

 side by side. To the one, maggots were added, while the other 

 was kept covered with wire gauze to prevent flies getting to it 

 and blowing it. It was moistened occasionally with water to 

 prevent it from drying up. When both were similarly covered, 

 blow-flies kept continuously buzzing round and settling upon the 

 gauze coveiing of the former, while none or very few came to 

 the latter. 



Other substances were also tried, with like results, though 

 their attractiveness without maggots varied with the diflerent 

 substances, and with the same substance at difi'erent stages. 



Since this was seen to be the case, pepsin was tried to see if it 

 acted in the same way. It was found, however, that both fish 

 and meat after they had been acted upon by pepsin in the 

 presence of hydrochloric acid, attracted fewer flies than did the 

 controls of meat or fish alone. Tlie flies used were chiefly Lucilia. 

 Peptone was also tried, both moistened with water and mixed 

 with bread ; sometimes maggots were also added *. A variety 



* The maggots did not thi-ive in these mixtures. They appeared unhapp.v and 

 restless, oftfin escaping out of the dishes. 



