148 OLIVE C. LODGE. 



time.* The baits (casein mixture or honey) were smeared in thin layers upon 

 the outsides of the test tubes (a-a) which were kept at a constant temperature for 

 a length of time, by circulating water throughout the series of vessels by means of 

 siphons ; the rate of flow being regulated by stop-cocks. The water in the flasks 

 (b-b) was heated or cooled as required, and flowed into the test-tubes (a-a) and 

 heated or cooled the baits. The flasks were kept filled by water from the breffits 

 (c-c). In order to keep the temperature of the test-tubes as constant as possible, 

 it was necessary to allow only water of constant temperature to enter them. This 

 was done by regulating the amount of water flowing into the flasks from the vessels, 

 and from them into the test-tubes. The water escaping from the test-tubes was 

 also regulated, so that the quantity of water entering and leaving the test-tubes 

 and flasks neutralised each other, and thus kept the temperature of the test-tubes 

 and baits constant. In this way it was possible to keep the baits at different 

 temperatures and to compare the numbers of flies feeding upon them with those 

 on the control (at room temperature). They were kept under observation, and the 

 numbers of flies feeding on each of the baits at different temperatures was recorded 

 at short intervals during the day. 



The results obtained from a number of experiments showed that the largest number 

 of flies (Musca) came to feed on the baits at temperatures of 38°-48° C, while the 

 highest and lowest temperatures at which they were seen to feed on the baits were 

 respectively 55°-58° C. ; and 10°-13° C. 



Humidity. 



It is generally supposed that the amount of moisture in the atmosphere makes 

 a difference in the attractiveness of certain substances for flies and affects the numbers 

 coming to various baits, formalin in particular being apparently so affected. A 

 number of experiments were made to test this, which were chiefly carried out in the 

 greenhouse. But owing to various practical difficulties and also to lack of time, 

 it was not possible to draw any definite conclusions. The general impression was 

 that most foods, especially when very moist, were more attractive to the house-flies 

 on dry than on wet days. 



Again flies, and more particularly blow-flies, were found to be able to stand a 

 greater amount of moist than dry heat. The blow-flies bred in the greenhouse 

 (which became very hot and dry in the day-time in the summer) throve if the air 

 was kept moist, but died if it became dry. This applies to the maggots as well, 

 but was more marked in the case of the flies. Without water house-flies were able 

 to live only one or two days. 



Experiments to discover the cause of the reactions of flies to the various 



sense-impressions. 



Experiments were made with a view to discovering what causes flies to react as 

 they do to sense-impressions, and whether sight or smell plays the principal part 

 in attracting or repelling them to baits, etc. ; therefore, (a) various foods were 

 covered in different ways, (b) the eyes of the flies were painted over, and (c) their 

 antennae cut off ; and their behaviour was then noted when the various substances 

 were fed to them. 



*My thanks are due to Mr. F. M. Howlett for many suggestions in the setting-up of 

 this apparatus. 



