77 



We consider this hand dropping 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 chemicals. 



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 empt}^ 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 fellovz-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 destroj^ armored scale insects. 

 For convenience we express the strength of gas as the ratio of the 

 number of ounces of cyanide used to the number of cubic feet in 

 the space inclosed. Gas at a strength of 1 ounce to 450 cubic feet 

 appears to be uniformly fatal to scale insects {Asjoidiotus aurmitii, A. 

 nerii, A. rajxix, 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 cubic feet gas; and the proj^ortion 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 photographic 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 exx)Osed. 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- 



