FORMALDEHYDE AS A POISON FOR HOUSE-FLIES. 



53 



in two-inch saucers with blotting-paper covers. Each series was continued for 

 two days and the cylinders were kept as wet as possible, though in several cases 

 they dried somewhat towards the end, with a corresponding increase in the death- 

 rate. The controls were on a dry table with muslin tops to the cylinders, the 

 relative humidity being about 76 per cent. The fourth experiment in Table VII 

 is taken as a control for the saturated conditions with unbaited formaldehyde. 

 To obtain a proper estimate the percentages dead at the end of twenty-two hours 

 should be studied. Another series carried out in precisely the same way, but with 

 bread-water as a bait instead of sugar, gave very closely similar results and will 

 therefore not be detailed. 



Table IX. 

 The effect of Baited Formaldehyde compared under Wet and Dry Conditions. 





1 



1 

 1 





Percentages dead after : 



Solution 



Conditions 



No. of flies 





5 hrs. 



22 Ims. i 48 hrs. 



N o bait, formaldehyde 1 % 



wet 



90 





17 





Sugar 5% 



dry 



38 



32 



97 



100 



?» »> )' »» 



wet 



34 



3 



35 



79 





7-5% 



dry 



32 



44 



91 



100 





J> 9» J> 



wet 



28 



3 



23 



69 





5-0% 



dry 



21 



43 



100 



100 



« 



>j >» >> 



wet 



23 



4 



22 



78 





O.KO/ 

 j» M ^ ^ /O 



diy 



19 



21 



79 



100 



' 



J> >» >> 



Avet 



17 







6 



82 



Humidity and the use of formaldehyde on ships. 

 Lt.-Col. W. Byam, R.A.M.C., reported that while he found formaldehyde very 

 effective on board ship, it failed to be of use in Egypt. This is in accordance with 

 the variations in the accounts of its utility. That used in Egypt was possibly too 

 acid. Experiments w^ere devised to discover what its effect would be on board ship 

 where the atmosphere is moist, but not necessarily saturated, and where most of 

 the available water is salt, owing to all the woodwork being saturated with this 

 substance. 



(1). A cyhnder was washed inside with 10 per cent, salt solution, flies were intro- 

 duced and blotting-paper soaked in the salt solution placed above and below ; a 

 shelter was erected over the poison dish to prevent the salt water dripping in. A 

 control was set up, fresh water being used instead of salt solution. It was foimd 

 that the flies were poisoned about twice as rapidly in the one with salt water as in 

 the one with fresh water. 



(2). This was carried out in cylinders, a bait being used in the poison which was 

 soaked up in jars of sand (area 2*5 sq. in.) that were placed in dishes of sand (area 13*5 

 ■sq. in.) wetted in one case with 10 per cent, salt solution and in the other with water. 

 The atmosphere would be very moist from the vapour given off by the wet sand. 



