82 



several mice were found dead. A large number of the roaches were 

 again collected and kept in a cage until the following day, Avlien 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. The dose 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 Avere dead, Avith the 

 exception of a few roaches which had secreted themselves between the 

 sash and frame of a loosely fitting Avindow, and had thus secured 

 enough pure air to iDrevent their being killed. 



To convey an idea of the injur}' caused by tlie presence of large 

 numbers of roaches in this laboratory', it might be stated that, fre- 

 quently preceding this last fumigation, lohotographic plates placed on 

 racks to dr}- 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 fumigation no inconvenience has been caused by the work 

 of roaches or mice. 



By aid of the results obtained from the above experiments, together 

 with otir jjresent knowledge of the action of hydrocyanic-acid gas in 

 exterminating greenhotise and scale insects, it may be stated that a 

 dwelling, office, warehouse, or anj^ building may be economically 

 cleared of all pests, provided that the local conditions will jDermit the 

 use of this gas. It probably would be dangerous to fumigate a btiild- 

 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 ptit out all fire in an 

 inclosure before fumigating. Hydrocyanic acid in all of its forms is 

 one of the most violent poisons known, and no neglect shotild attend 

 its use. There is probably no sure remedy for its effects after it has 

 once entered the blood of an}- of the higher animals. When cyanide 

 of potassium is being tised it shotild 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 Avith court-plaster to j)reA'ent the 

 gas coming in contact Avith the flesh or the possibility of a small par- 

 ticle of the solid com]30und getting into the cut, Avhich Avould cause 

 death b}- poisoning AA'ithin a feAv minutes' time. 



Hydroc3'anic-acid gas should not be used in closely built apart- 

 ments Avith single Avails betAveen, as more or less of the gas Avill pene- 

 trate a brick Avail. An inexi:)erienced i^erson sliould iieA'er use cyanide 



