THE HOUSE-FLY 29 



have never tried this and have heard of reported failures. 

 It would seem as though the amount to be used would 

 depend upon the size of the room. 



Minis culicide. This is also useful in killing flies as 

 well as mosquitoes. It should be used exactly as is 

 described in the chapter on methods of protection from 

 mosquitoes. 



Bichromate of potash. This is a substance often used 

 to kill flies. It is not a virulent poison and, therefore, 

 little danger is incurred in putting it about the room. It 

 should be dissolved in water at the rate of one part of the 

 potash to two of the latter and then set about in shallow 

 dishes. If the room can be darkened except one window 

 and the solution put on the ledge of this one, in the light, 

 the results will be quicker. This substance has not always 

 given good results. 



Formaldehyde. One of the best solutions for attract- 

 ing and killing flies is a dilute mixture of formaldehyde 

 (40 per cent) with water and milk. A tablespoonful in 

 a pint of equal parts of water and milk will attract the 

 flies and kill large numbers of them. The mixture should 

 be poured into shallow dishes, soup plates for instance, and 

 a crust of bread dropped into the middle of the dish for 

 the flies to light upon and to facilitate their feeding. If 

 the shades of all of the windows in a room but one are 

 pulled down and a plate of this mixture set in the light, 

 the flies will be attracted and killed. We have cleared 

 a dining-room of every fly in an afternoon in this way. 



Formaldehyde will not prove so effective in dining- 

 rooms or kitchens where there is food, water, or milk to 

 which the flies have access. It will be most successful 

 where it is the only liquid they can get to drink. For- 



