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the use of the same remedy for household pests. It is now no longer 
a theory but an established fact that 0.10 gram of 98 per cent pure 
cyanide of potassium volatilized in a cubic foot of space will, if allowed 
to remain for a period of not less than three hours, kill all roaches 
and similar insects. 
The experiments which led to this conclusion were made in a small 
building which is used for laboratory purposes by the Division of 
Botany. This structure has for some time been infested with several 
insect pests, the more numerous and troublesome of which was the com- 
mon cockroach ( Periplaneta americana). The building consists of one 
story and basement, the upper part being rather loosely built, as it is 
ceiled throughout with matched lumber. This method of construction 
provides numerous hiding places for the insects, and also renders 
fumigation difficult by permitting the gas to escape too quickly. 
Within the building are several sources of moisture, a rather high 
and constant temperature is maintained in some of the rooms, and 
large quantities of seeds and substances that serve as food for insects 
are stored, making conditions well adapted to the development of 
cockroaches. 
During the early part of last year the roaches became so numerous 
as to be a detriment to the work of the laboratory, and it was necessary 
to adopt some means of checking them. On the evening of May 10, 
1900, the building was closed, and after opening up the interior of the 
rooms as much as possible the entire structure was fumigated experi- 
mentally with about 0.08 gram of 98 per cent pure cyanide of potas- 
sium per cubic foot of space. The gas was allowed to remain during 
the night, or until it gradually escaped. When the rooms were 
entered the following morning there remained a perceptible odor of 
the gas, but this soon disappeared after opening the windows and 
doors. The ledges and window sills were strewn with dead house-flies 
and the floors bore abundant evidence of the effect of the gas on 
roaches. Not asingle insect that showed indications of remaining life 
was to be found in the building. About a quart of the flies and 
roaches was gathered up and placed in a cage, where they were allowed 
to remain until the following day, when two roaches showed signs of 
life by slow movements. These, however, could not walk when placed 
upon their feet, and subsequently died. 
For some time after this fumigation no roaches were to be found in 
the building, but eventually the eggs that had been previously deposited 
hatched and developed, adults were carried in from other buildings, 
ete., until in March of the present year the roaches had again become 
so numerous as to be a nuisance and a detriment to the work of the 
laboratory. The building was again treated with cyanide gas, this 
time at the rate of 0.10 gram per cubic foot of space, but it was allowed 
to remain only fifty minutes, when the windows were opened and the 
gas permitted to escape. The roaches were strewn over the floors and 
11825—No. 31—01 
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