62 



Methods (a) and (6) were most effective, owing- to the pro- 

 longation and certainty of contact, and the insect rarely escaped 

 death; (c) and (d) were not so successiul, some insects recovering- 

 and feeding and depositing- ova in contact with the powder; (e) 

 did not prove a satisfactory method of trial. The certainty with 

 which a g-iven powder will kill bed-bugs was fonnd to depend 

 chiefly upon: (1) fine subdivision of the powder; (2) its dryness; 

 (3) its lightness. Methods (a) and (6) will kill bug-s with great 

 certainty, the action being- apparently, in most cases, purely 

 mechanical. If the bug be sprinkled with the powder, it becomes 

 coated over with fine particles, adhering to the body, antennae and 

 legs. After struggling- for a time the insect turns over on its 

 back and in this position it struggles until it dies, the period 

 varying from a few minutes to several days. Details as to the 

 action of several powders are given. The author says in regard 

 to these insect powders in general, that they are very fatal to 

 bugs, and will destroy them with considerable certainty if applied 

 by methods (a) and (h), while they are partially successful by 

 methods (c) and (d). MetJiod (e) clearly shows that these powders 

 must fail radically to exterminate the bugs under natural con- 

 ditions, as there is nothing to compel them to come out of their 

 hiding- place and seek food, and consequently they escape the 

 powders which are strewn on their supposed path. The powders 

 appear to have no effect upon the eggs. The larvae hatched from 

 eggs covered with the powder generally die. 



Besides the above, various other powders were tried : French 

 chalk, pulv. rhei., pulv. jalapae, Dalmatian flower powder, pulv. 

 cort. ulmi., pulv. cinchonae, pulv. sod. brom., pulv. embel., 

 pulv. acid tannic, pulv. amyli, and barium sulphate. Some of 

 these powders had marked effects on adults and newly hatched 

 bugs, when applied by methods (a) and (6). Dalmatian flower 

 powder and fine French chalk are good insecticides ; pulv. 

 cinchonae quickly renders bed-bugs incapable of progression. 



A five per cent, solution of carbolic acid killed bugs in ten 

 minutes, immersion for a shorter time only killing- a small pro- 

 portion. A ten per cent, solution killed them in two minutes, 

 but after one minute five remained alive out of thirty. 



A solution of perchloride of mercury, one in a thousand, had 

 very little eff'ect. Less than two hours immersion killed none 

 and five and a half hours killed only one in five ; while a half 

 per cent, solution was almost equally ineffective, thirteen out of 

 twenty recovering after thirty minutes immersion. 



Paraffin oil in five seconds produced sufficient effect on ten bugs 

 tried that, after five seconds immersion, all ultimately died at 

 the end of twenty-four hours. Bugs are capable of walking over 

 wood smeared with paraffin, without harm. The author regards 

 paraffin as the most efficient of all the liquids tried. 



Chloroform vapour does not kill, unless the action is very pro- 

 longed (3 hours) ; the vapour of paraffin oil for eighteen hours 

 had little effect; carbonic acid gas paralyses the bugs but does 

 not kill them, all exposed to it recovered; coal gas killed in 

 fifteen minutes; hydrocyanic acid was rapid, and effective, but 

 too dangerous for practical purposes; sulphur dioxide invariably 

 killed in a few seconds. The experiments with this gas were 



