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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 i)0ssible 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 tliere remained a i3erceptible 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 a single 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 im 

 the building, but eventually the eggs that had been previously deposited 

 hatched and developed, adults were carried in from other buildings, 

 etc. , 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 



11823— No. 31—01 6 



