2 
Entomologists have long noticed that insects vary greatly in their 
susceptibility to cyanide fumes. The ordinary killing bottle used in 
making collections contains cyanide of potassium covered with plaster 
of Paris, which the fumes of the cyanide penetrate. Certain weevils, 
and especially such weevils as Lixus and Sphenophorus and other 
hard-bodied forms, will frequently be left overnight in a cyanide bottle 
and recover after being removed. It has been noticed also that in 
greenhouses certain insects recover. The experience gained, however, 
indicates that the use of hydrocyanic-acid gas in houses is successtul 
against cockroaches, bedbugs, fleas, clothes moths, ants, white ants, 
house flies, and other soft-bodied insects; and as these constitute the 
majority of the household pests, the use of the gas must now be con- 
sidered a standard remedy. Moreover, rats and mice are also killed by 
its use, and it fortunately has the effect of first causing these animals to 
rush out from their holes into the open, so that the subsequent annoy- 
ance of dead mice in walls and under floorings is not experienced. 
* Since the initial experiment against household pests in 1898 a great 
deal of experience has been gained in practical work by this Bureau. 
Many residences and public buildings and offices of this Department, 
stores, and schools have been fumigated, especially since 1901. This 
work has been conducted chiefly under the direction of Mr. Marlatt by 
Messrs. Busck, Pratt, Kotinsky, J. H. Beattie, and other members of the 
office force, and has given practically uniform success. Most of this 
work was done subsequent to the publication of Circular 46, second 
series, and is the basis for the present revision of that circular, which, 
however, has not been changed in essential details. 
Some entomologists recommend as a substitute for hydrocyanic-acid 
gas a substance which has been more or less effectively used, viz, car- 
bon bisulphid. The great danger in the use of this latter substance, 
however, from its extreme inflammability and the explosiveness of its 
vapor when confined, renders it perhaps less available and more than 
counteracts the danger to human beings from the use of the hydrocyanic- 
acid gas.! 
'To determine the availability of hydrocyanic-acid gas against the insect 
enemies of stored products or in granaries, some experiments were made during 
1898 and the spring of 1899 by Messrs. Marlatt and Chittenden, of this oflice, in 
the presence of Mr. D. G. Fairchild and others, against certain grain weevils and 
the Angoumois grain moth, but with imperfect success, although the proportions 
used were much greater than in Mr. Craw’s experiment. In his recent book on 
fumigation methods, Prof. W. G. Johnson states that he used the hydrocyanic- 
acid gas in a granary and storehouse in June, 1899, using it at the rate of 0.1 
gram of cyanide per cubic foot of space. The granary was affected by weevils, 
and, from the report of the owner, it appears that most of the latter were de- 
stroyed, though many escaped. During the same month in an Ohio mill another 
experiment of this kind was carried on under Professor Johnson’s instructions. 
The owner considered the experiment to be ‘‘a most grand success.’’? The 
Mediterranean flour moth and certain granary beetles were destruyed. There is 
still some doubt, however, as to its efficiency under granary and mill conditions, 
and further experimentation is needed. 
