328 A, C. JACKSON AND H. M. LEFROY. 



As our object was to find as quickly as possible a poison to replace arsenic, which 

 is used at 2 per cent., we used our substances at that strength, and we went no 

 further if the flies fed freely and did not suffer. If there were signs of poisoning, 

 the substance would be tried up to 5 per cent, and down to -02 per cent., if 

 necessary. The results obtained with substances found to be poisonous are 

 summarised below; where no strengths are given a 2 per cent, mixture was 

 used. 



To help others and to obviate testing ineffective substances, we attach below 

 a complete classified list of all the substances tested in 1915-1916 by Miss Lodge, 

 and in 1917 by ourselves, with the results. 



Methods. 



The experiments were carried out in the Fly Room at the Imperial College of 

 Science, which had been set apart for the breeding and keeping of flies {Muscu 

 domestica), so that a continuous supply of the insects for experimental purposes 

 was insured. A weighed amount of the chemical to be tried as a poison was added 

 to a measured quantity of standard 20 per cent, sugar solution ; if the chemical 

 was insoluble, it w^as made into as fine powder as possible and mixed up w^ith a 

 known quantity of food mixture. The food mixture used was approximately 2 

 parts casein, 2 parts banana and 1 part molasses, niLxed with water to form a 

 paste. The solution or food mixture was then placed under a glass cylinder with 

 a muslin top ; if a solution, a piece of filter paper was placed in the dish to enable 

 the flies to feed more easily and prevent them from being drowned. The requisite 

 number of flies was then caught by means of a wire balloon-trap and released in 

 the cyUnder, the hour at which they were released being noted. In some cases the 

 flies fed very soon, in others it was an hour or two before many flies were observed 

 feeding. This depended on (1) whether the flies were hungry or not, (2) whether 

 the chemicals employed were liked or disliked by them. The dead flies were 

 counted about 5 p.m. on the day the experiment was started (if the experiment 

 had been started early that morning, a count was also, in some cases, made at noon), 

 and at 10 a.m. next day. If no flies, or only a few, were found dead at this last 

 count, the chemical was considered to have failed and w^as placed in Class III. If 

 about half the flies were dead, the chemical was regarded as moderately good and 

 placed in Class II. If all or most of the flies were dead, then the chemical was 

 classed as good, placed in Class I, and further experiments with it, at different 

 strengths, were carried out in order to discover the lowest strength which killed 

 flies effectively ; also the point at which the chemical ceased to be harmful 

 to flies. 



Some of the chemicals tried were more or less distasteful to flies. Thus, 

 ammonium 3 : 5 ortho-dinitro-cresylate, in strengths of from 2 per cent, down 

 to '05 per cent, in sugar solution placed out on the bench, was not liked by flies ; 

 though they came readily to '025 per cent, in sugar solution, which however had 

 no poisoning effect on them. To ammonium fluoride and ammonium iodate at 

 the same strengths they came readily, the 2 per cent, strengths being quite as 

 much hked as the lower strengths. 



