5 
Formaldehyd gas kills mosquitoes whenever the gas comes in direct 
contact with them in sufficient concentration and for a sufficient length 
of time. When exposed directly to the gas produced by any of the 
methods commonly used for disinfecting purposes, the mosquitoes die 
within few minutes. If the insects are confined in a bell jar and some 
formalin is dropped inside, they soon show signs of agitation and shortly 
drop down, dead. They may, however, live over night in a very feeble 
atmosphere of the gas. 
The conditions necessary to obtain this direct contact, however, can 
not always be obtained in actual, practice. Booms are frequently not 
tight enough to obtain the concentration of the gas required. The 
mosquitoes can not be held in direct contact with the gas, for their 
sense of self-preservation helps them to escape. The period of irrita- 
tion, lasting several minutes even in the bell jar, enables the insects to 
hide* in available places, such as the folds of garments, hangings, or 
fabrics, or in the cracks and crevices where the gas only reaches in a 
diluted form. If the room is not thoroughly sealed, some of the 
mosquitoes will surely get away, for their instinct in finding tiny 
avenues of escape is remarkable. The escape of one infected mosquito 
might be the spark that would rekindle an epidemic. 
In general, it may be stated that to succeed in killing mosquitoes in a 
closed space with formaldehyd gas, the following definite requirements 
are essential. A large volume of the gas must be liberated quickly, so 
that it may diffuse to all portions of the room in sufficient concentra- 
tion. The room must not have cracks and chinks where the insects 
will breathe the fresh air entering, especially if these openings are to 
windward. The room must not have heavy drapery, clothing, bed- 
ding, or other fabrics, so disposed that the insects may hide in the folds, 
away from the full effects of the gas. 
Four methods of evolving formaldehyd gas were used, namely : 
1. The sheet method. 
2. The Kuhn lamp. 
3. The Trenner-Lee formaldehyd disinfector. 
4. The autoclave. 
THE SHEET METHOD. 
This method was applied by hanging sheets in the room and spraying 
formalin (40 per cent) upon them by means of Dr. Behni’s formaldehyd 
sprinkler. The solution was sprinkled on the sheet in small drops in 
order to facilitate evaporation and prevent polymerization. For bac- 
terial disinfection, 5 ounces of the solution are prescribed for each 1,000 
cubic feet of space, the time of exposure to be not less than five hours. 
No. 1. 
In a room of 2,000 cubic feet capacitj*, 4 sheets were hung on cords 
crossing the room. Twenty ounces (600 c. c.) of formalin (40 per cent) 
