62 CAPT. LL. LLOYD. 



This form of trap may be used under cover or outside when it is not raining. The 

 paper should be renewed every third or fourth day in any case. A more permanent 

 form may be made from plaster of Paris or some other durable material, porosity 

 being an essential. The stem in this case is circular and should be in one piece with 

 the top, or fit into it very tightly, otherwise the fluid will not rise. It may be 

 necessary to soak this trap in water occasionally and dry it. 



These traps have been submitted to the very severe tests of being placed near 

 dishes of the food which has been found most attractive to house-flies, casein, banana 

 and bread, mixed and wetted. One trap with the top made of plaster of Paris was 

 placed about a foot away from a large dish of this material, and in three days poisoned 

 1800 flies, which were found on, or within a few inches of it. After further neutra- 

 lisation it became effective again and remained so for ten days, about half the original 

 fluid (200 cc.) having been used. Another one, with the top made of filter paper two 

 inches in diameter, was placed in a corner of the fly room, and was active for ten days 

 imtil it was removed, the paper top having been renewed once ; 1,560 flies were found 

 dead around it. A third one with a paper trap was still active at the end of a month. 

 Whether a trap is still effective may be determined by sweeping away the dead flies 

 from its vicinity. If no more flies accumulate, and there are still flies about, the 

 fluid has probably become acid and should be renewed, as it will not be found worth 

 while in practice to neutralise it again. The traps should be placed wherever flies 

 are numerous, especially near rubbish bins, in stables, near manure heaps, in kitchens 

 and latrines. Observation will show which are the best positions. 



Comparison with other Poisons. 



Formaldehyde as a fly poison was not tested against sodium arsenite, but it has 

 two great advantages over it : it is safe and it is more economical. With 2 per cent. 

 sodium arsenite solution 10 per cent, sugar is recommended, while formaldehyde only 

 requires a quarter of that amount. Tlie use of sodium arsenite would always be 

 dangerous to man and to domestic animals, especially if issued to the general 

 pubhc. That the poison used shall be safe in any hands is a great desideratum. 



The action of formaldehyde was tested against that of sodium fluoride, recently 

 recommended as an effective fly poison (Jackson and Lefroy). Formaldehyde (5 

 per cent.) and sodium fluoride (1 per cent.) in saucers were placed in two separated 

 halves of a deep glass dish, equally lighted and heated. No baits were used in either. 

 After twenty-four hours in the formaldehyde section 650 flies were dead as against 234 

 dead in the sodium fluoride section. As more might have escaped from the section 

 containing the fluoride than from the other section, a control comparison was made 

 with cyhnders of flies, four containing as poison 1 per cent, sodium fluoride with 3 per 

 cent, sugar, and four containing the formaldehyde mixture recomr?,ended above. 

 Notes were made of the death-rate and it was found that there was no appreciable 

 difference in the actions of the two poisons. The results are summarised in Table 

 XV. However from the first experiment it is seen that flies poisoned travel less from 

 the formaldehyde than from the fluoride, which is an advantage. Authorities differ 

 as to whether sodium fluoride is a poison to man, but as it is used in food preserving 

 it is certainly not a very dangerous substance. 



