78 



mens were recorded to sur\aYe the strength of 1 to 235 for one hour 

 and three for 1 to 235 for two hours, but in these instances the speci- 

 mens Avere all destroyed at the end of twenty-four hours, it not at the 

 time being known that any might subsequently recover. In every 

 case all of the bugs were stupefied by the gas, and none were noticed 

 to again become active until at least two hours had elapsed. AYith the 

 1 to 150 strength for an hour, none showed signs of life at the end oi 

 five hours, but twenty hours later one could crawl and another feeblj^ 

 move its legs, and on the following day a third responded when probed 

 lightl}'; at the end of a week the one seemed fully recovered while 

 the others were still too weak to move about. It is evident from 

 these tests that 1 to 155 gas for an hour is too weak for room fumiga- 

 tion since not all full}^ exposed bugs may be destroyed. It is only 

 fair to mention, however, that in practice we have known 1 to 150 

 gas giA'e seemingly perfect results in a number of instances. At 

 other times Avliile greatly decreasing the pest its use has not been 

 satisfactory. 



The eggs of bedbugs seem to be devitalized with the use of about 

 the same strength of gas as is fatal to the active stages, but we have 

 had little opportunity to make observations on this phase of the prob- 

 lem and therefore speak with reserve. Seven eggs laid within thirty 

 hours of their exposure failed to hatch after treatment for two hours 

 in 1 to 125 gas, the space in this case being a fairh" tight room in a 

 plague house and the eggs being fully exposed ; nineteen eggs six days 

 old failed to hatch after exposure for one hour in 1 to 150 gas in the 

 dark room referred to above. Check eggs were not preserved. N^o 

 eggs hatched in numbers of seemingly sound ones taken from treated 

 railway coaches at the beginning of that work. It may seem strange 

 that eggs should be devitalized by the gas, but in experiments con- 

 ducted here three years ago it was determined that scale insect eggs 

 {Diaspis ijentagona and other species) succumbed to 1 to 300 gas; in 

 fact, it vras observed that eggs of a species of Dactylopius lost their 

 vitality from an hour's exposure in the strength of gas mentioned 

 when adults escaped death. Check lots of eggs of the different kinds 

 exposed hatched. 



The common roach {Ectobia germanica) succumbs to overnight 

 treatment with 1 to 100 gas. The kitchen and scullery of one of the 

 Cape Town clubs swarmed to an almost incredible extent with this 

 insect. The spaces were treated with the strength intimated, and in 

 the morning not less than a half bushel of dead roaches were swept 

 up. About fifty that bore ootheca were boxed and brought to the office 

 and no eggs hatched from them ; there was no check test, however, 

 to determine if such eggs Avould hatch Avere the females otherAvise 

 destroj^ed. 



The fleas on a dog confined in a room, treated for an hour AA'ith 1 to 

 180 gas, Avere all destroyed; one hundred Avere remoA^ed and kei)t 



