HOUSE-FLY INVESTIGATIONS. 495 



Brown sugar + Kepler's Malt Extract 1-8 



Malt Extract , 1-8 



Casein + water (boiled together) 1-8 



,, + banana + water 1-4 



„ +bread + „ 1-tj 



Bird's Custard Powder + boiled milk 1-4 



„ „ „ + „ water + brown sugar ... 1-8 



Brown sugar + starch (boiled together) 1-12 



Starch + boiled water 1-4 



Casein + brown sugar + dried blood + water 1-8 



„ + „ „ +beer + water 1-4 



Condensed milk 1-6 



„ „ +jam 1-6 



Bread + Dutch cheese + water 1-6 



" Ridge's Food " + water 1-5 



„ „ + brown sugar + bread + water 1-5 



The main conclusions arrived at from these experiments on 

 house-Hy baits were : — 



(1) That the most satisfactory baits consisted of — 



(a) Mixtui'es of casein, sugar, or some other sweet stufi" and 



water, with or without banana, in approximately 

 equal proportions, to which stout or beer can be addecl, 

 iu which case they became immediately attractive, 

 otherwise one or two days elapsed before the most 

 attractive stage was reached * ; 



(b) Horlick's Malted Milk mixed with water ; 



(c) Banana, especially when over-ripe ; 



(d) Custard puddings ; 



(e) Cornflour, milk, and sugar ; 



(/) Bird's Custard Powdei-, milk, and sugar, etc. (vide list J). 



(2) There are advantages in using the casein mixtures rather 



than the other attractive baits in 



(a) the comparative cheapness of casein (Is. Ad. per lb.) and 

 (6) the little trouble the baits take to prepare, the ingredients 



simply requiring to be mixed into a paste with a little 



water ; 



(c) The length of time they remain attractive (7-10 days as 



compared with the 2-3 days of beer and sugar) ; 



(d) The absence of any disagreeable smell when the casein is 



mixed with sugar, golden syrup, banana, etc.f 



* In November and December, however, the house-flies at the Imperial College 

 came in swarms to feed on the casein mixtures as soon as they were placed on the 

 bench. The}' even came to bread only. Was this because of the dift'erence in the 

 hunger-states of the flies at these different times, or were the casein mixtures more 

 attractive when simply put out on the bench without being covered by a trap ? 



t Sugar, beer, alcohol, etc. had another advantage, as they appeared to preserve 

 the baits from going mo\ildy, which often happened when casein was used alone, 

 though this did not necessarily prevent them from being attractive. The great 

 advantagewas, however, that they kept them from giving off the most offensive smell 

 which was the case when casein and water, and casein, water, and bread were used. 



