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several mice were found dead. A large number of the roaches were 
again collected and kept in a cage until the following day, when it was 
found that fully 10 per cent of them had not been killed and were as 
lively as before treatment. The mice, however, showed no indications 
of life. Thedose had been sufficiently strong, but had not been allowed 
to remain long enough to kill the more resistant of the roaches. 
The third and most satisfactory experiment of the series was con- 
ducted on the evening of June 20, 1901, when an application of 0.10 
gram per cubic foot was allowed to remain in the building overnight. 
On the following morning the gas had not entirely escaped, and house- 
flies, centipedes, spiders, cockroaches, and mice were dead, with the 
exception of a few roaches which had secreted themselves between the 
sash and frame of a loosely fitting window, and had thus secured 
enough pure air to prevent their being killed. 
To convey an idea of the injury caused by the presence of large 
numbers of roaches in this laboratory, it might be stated that, fre- 
quently preceding this last fumigation, photographie plates placed on 
racks to dry and allowed to remain on a table for one hour were com- 
pletely ruined by having films eaten from the glass; packets of seeds 
stored in mouse-proof tin boxes were so eaten as to allow the seeds to 
escape, and in many cases the seeds themselves were destroyed. 
Since this fumigatlon no inconvenience has been caused by the work 
of roaches or mice. 
By aid of the results obtained from the above experiments, together 
with our present knowledge of the action of hydrocyanic-acid gas in 
exterminating greenhouse and scale insects, it may be stated that a 
dwelling, office, warehouse, or any building may be economically 
cleared of all pests, provided that the local conditions will permit the 
use of this gas. It probably would be dangerous to fumigate a build- 
ing where groceries, dried fruits, meats, or prepared food materials of 
any kind are stored. Air containing more than 25 per cent of the gas 
is inflammable, therefore it would be well to put out all fire in an 
inclosure before fumigating. Hydroeyanic acid in all of its forms is 
one of the most violent poisons known, and no neglect should attend 
its use. There is probably no sure remedy for its effects after it has 
once entered the blood of any of the higher animals. When cyanide 
of potassium is being used it should never be allowed to come in con- 
tact with the skin, and even a slight odor of the gas should be avoided. 
Should the operator have any cut or break in the skin of the hands or 
face, it should be carefully covered with court-plaster to prevent the 
gas coming in contact with the flesh or the possibility of a small par- 
ticle of the solid compound getting into the eut, which would cause 
death by poisoning within a few minutes’ time. 
Hydrocyanic-acid gas should not be used in closely built apart- 
ments with single walls between, as more or less of the gas will pene- 
trate a brick wall. An inexperienced person should never use cyanide 
