iM 
We consider this hand drepping of the cyanide into vessel after 
vessel far safer and much more expeditious than methods of drop- 
ping which involve the use of strings manipulated from without the 
space. The cloth bag facilitates the dropping act, and retards but 
for a brief space the evolution of the gas. Curiously the cloth is 
sometimes practically uninjured by the chemieals. 
Great care is always needed when the spaces are opened for venti- 
lation to keep out inquisitive parties, and it is then that the responsi- 
bility of the operator is greatest. On still days the generation of 
heat by fires and the burning of large lamps is useful to expedite 
renewal of the air. The gas soon dissipates from empty rooms, but 
clings to bedding somewhat tenaciously; hence several hours’ airing 
is desirable if severe headaches are to be avoided. It has been noticed 
that persons with weak lungs, of which there are many in some 
prisons among long-term convicts, suffer painful inconvenience from 
traces of gas unnoticed by their healthier fellow-prisoners. 
The public department in charge of plague work administration 
has begun to make limited use of the gas for dwelling fumigation to 
effect the riddance of bugs, fleas, and lice. The procedure followed 
is the same as in jail work and the same strength of gas is used; as 
prolonged control over the premises can be had, the exposure is made 
longer, as overnight. 
These various governmental uses of the gas have not been inaugu- 
rated without experimental demonstration of its efficiency. Our 
tests, conducted in tight spaces, have shown that much stronger gas 
is required to destroy bedbugs than to destroy armored seale insects. 
For convenience we express the strength of gas as the ratio of the 
number of ounces of cyanide used to the number of cubie feet in 
the space inclosed. Gas at a strength of 1 ounce to 450 cubic feet 
appears to be uniformly fatal to scale insects (Aspidiotus aurantii, A. 
neru, A. rapax, and Diaspis pentagona) exposed to it for an hour, 
but to have little, if any, effect on bedbugs. <A portion of a given 
number of bugs is destroyed by an hour’s exposure to 1 ounce to 
250 cubie feet gas; and the proportion destroyed increased with 
increase in the strength of the gas and the period of the exposure. 
Our main series of tests with bugs was made in a photographie dark 
room approximating 235 cubic feet in capacity. The temperature of 
this space varied in the different tests from 56° to 64° F. Care was 
taken to have nothing present that might absorb and thus weaken 
the gas, and only active, healthy-looking specimens of the insect 
were exposed. Fifteen specimens were used for each test, and these 
inclosed in bags of gauze suspended at mid height on the side of the 
room opposite where the generating vessel stood. Eight specimens 
survived 1 ounce to 190 cubic feet for an hour, and three, 1 to 155 for 
the same period, but none 1 to 155 for two hours; these effects were 
determined by observation extending over a week. Only three speci- 
