79 • 



Tinder observation for a week to make certain that the result was as 

 it appeared to be. Lice (Hcematopinus spp.) on rats confined in the 

 same space were also destroyed. So were several kinds of ants and 

 the common house fly; but not one of several hundred specimens of 

 various kinds of ticks, and onlj^ 40 out of 57 bedbugs. Ticks are the 

 least -susceptible to the gas of all the creatures we have exposed. 

 Adult Argas persicus, Amhlyomma hebrcBum, and BMpicephalus 

 evertsi have been exposed in large numbers to 1 to 150 gas for two 

 hours without a single specimen manifesting injury. A score of 

 A. hehrcBum thus treated were a month later, along with as many 

 more fresh specimens, exposed for an hour in 1 to 80 gas, and every 

 specimen came through this severe test seemingly more active than 

 before. Eight long-starved R. evertsi exposed to this strength were 

 much affected, 4 of them being killed and the other 4 greatly enfeebled. 

 It may be of interest to mention that cultures of Bacillus pestis, the 

 plague organism, exposed by replacing the customary cotton plug with 

 a covering of gauze, were unaffected at this strength and in weaker 

 strengths. This bacterium is accounted easy of destruction by ordi- 

 nary disinfectants. 



In the practical application of the gas we consider it advisable to 

 remove all water and all moist substances that might absorb the gas 

 and thus affect its efficiency by decreasing its strength. Water and 

 meat that have been exposed to the gas should be regarded as danger- 

 ous for consumption. We purposelj^ exposed meat and water to 

 extremely strong gas to see if the/ were really rendered poisonous. 

 Both proved quicklj^ fatal ^.o dogs which began to partake of them. 

 Meat exposed and then allowed to air for a few days proved harmless. 

 Flour exposed and afterwards made into bread was eaten by one of 

 us with impunity. 



The gas may be the most reliable agent for the destruction of insects 

 within a confined space that we have, but in general it is a mistake to 

 consider it an infallible eradicator. The extent to which insects in a 

 sjjace are protected by the character of their coverings can be deter- 

 mined only by experiment, and then only roughly. Individuals 

 among scale insects in masses on their food plants resist strengths of 

 gas far in excess of what is uniformly fatal to isolated specimens of 

 their kind. This we have observed in the orchard and demonstrated 

 in the laboratory. As with the adults of scale insects, so with the 

 eggs. We have found that the eggs at the end of the large ovisac of 

 Icerya purchasi are destroyed by 1 to 300 gas, while those deep in the 

 mass remain unaffected by 1 to 200. From experience we have come 

 to consider it inadvisable to relj^ on strengths of gas inferior to 1 to 

 100 for the destruction of bedbugs or to have the exposure less than 

 two hours. Under exceptional circumstances eA^en this great strength 

 has been found untrustworthy^ Active bedbugs were taken from 

 within door casings of a jail after the surrounding space had been 



