(a) 
under observation for a week to make certain that the result was as 
it appeared to be. Lice (Hematopinus 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 only 40 out of 57 bedbugs. Ticks are the 
least susceptible to the gas of all the creatures we have exposed. 
Adult Argas persicus, Amblyomma hebreum, and Rhipicephalus 
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. hebreum thus treated were a month later, along with as many 
more fresh specimens, exposed for an hour in | 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 
muchaffected, 4of 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 purposely exposed meat and water to 
extremely strong gas to see if they were really rendered poisonous. 
Both proved quickly fatal to 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 
space 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 ovisae 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 rely 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 even this great strength 
has been found untrustworthy. Active bedbugs were taken from 
within door casings of a jail after the surrounding space had been 
