124 ASSOCIATION OF ECONOMIC ENTOMOLOGISTS. 



(5) The insecticide powder should be spread in the room before 

 bedtime, it being possible for the people to enter the room after said 

 powder has settled down. 



(6) There are some kinds of the. powders which are entirely ineffi- 

 cient; this is true of most of the powders sold by retailers in small 

 quantities, in envelopes or in boxes, at 5 cents or less. To obtain good 

 ones they should be bought at some reliable drug store and tried in 

 the way above explained. 



(7) In order to avoid a daily expense for powder, it is advisable to 

 close the doors and windows early, so that the mosquitoes will not 

 enter the apartments, and it will even be very useful to put a fine 

 wire screen upon the windows. Should any mosquitoes, however, 

 succeed in entering the rooms, they will be killed by the powder of 

 chrysanthemum, an operation to be performed only when the insects 

 happen accidentally to enter on account of the openings having been 

 shut too late or because of any other circumstance. 



(8) An excess of powder is quite unnecessary, and might even 

 result in injury to the inhabitants. 



Xote. — It has been said that the fine powder, in large quantities, 

 may become ignited when there is a candle in the room, but it has 

 never been proved that such is the case when onty genuine chrysanthe- 

 mum powders are used. In a fumigating room made of canvas, with 

 a capacity of 68 cubic decimeters, we blew a large quantity of genuine 

 chrysanthemum powder, a part of which fell upon the flame of an 

 alcohol lamp situated in the back of the room. The only powder that 

 burned was that which touched the flame directly, whereby was pro- 

 duced a kind of rain of small sparks ; but the fire was never communi- 

 cated to the remainder of the powder, and no explosion occurred. 

 This experiment may be made on a small scale with a candle, and thus 

 the above statement will be confirmed, while at the same time it will 

 be found out whether the powder contains any foreign matter which 

 is inflammable and dangerous. Where electric light is used such a 

 precaution is unnecessary. 



This manner of destroying mosquitoes has already been put into 

 practice. To that effect the commission of parasitology has distrib- 

 uted gratuitously several barrels of chrysanthemum powders under 

 the form of small samples. The consumption of powders has been 

 tripled, while the sale of the tablets, which only throw the insects 

 into a state of lethargy but are very objectionable owing to their 

 pungent fumes, was decreased. 



The species of mosquito which is most frequently found in the City 

 of Mexico and which invades the houses is Culex pipiens L. 



