456 MOSQUITOES 



rubbed on the face and hands if the mosquitoes are very per- 

 sistent, was found by Dr. Howard to last long enough through 

 the night to be effective against all mosquitoes except the yellow 

 fever species, Aedes calopus, which begins its attacks at daybreak. 



Elimination and Exclusion from Buildings. The second 

 means of controlling mosquitoes, by eliminating and excluding 

 them from dwellings, is of more permanent value than the first, 

 and should never be omitted while the process of mosquito 

 extermination is under way. 



One of the best methods of ridding houses of mosquitoes after 

 they are once in is fumigation, and this is also an indispensable 

 method of destroying hibernating mosquitoes in cellars, attics, 

 barns, etc. The substance used for fumigation must depend on 

 the kind of place to be fumigated, and on the conditions under 

 which it is done. The most thorough and certain method of 

 fumigation, when the place to be fumigated can be vacated, is 

 by the generation of hydrocyanic acid gas. A less dangerous 

 and equally effective method, but one which is inj urious to metals 

 and house furnishings is by the use of fumes of burning sulphur. 

 These methods of fumigation are described in Chap. XXII, pp. 

 383-386. 



Fumigants which are not dangerous to human beings can be 

 used effectively against mosquitoes since these insects do not 

 require such penetrating fumes as are necessary to destroy 

 hiding parasites, as bedbugs and lice. Pyrethrum or Persian 

 insect powder, manufactured out of the dried flower heads of 

 -certain species of chrysanthemums, is an effective fumigant of 

 this type; it can either be dusted into corners, blown into the 

 air of a room, or turned. Powdered jimson weed, Datura 

 stramonium, is recommended by Dr. Smith, eight ounces, mixed 

 with one-third its weight of niter or saltpeter to make it burn 

 more readily, being burned per 1000 cubic feet. " Minim's 

 Culicide " is a volatile liquid made of carbolic acid crystals and 

 gum camphor in equal parts by weight, which is effective against 

 mosquitoes, four ounces being volatilized by heating for every 

 1000 cubic feet of space. A fumigant which has come into great 

 favor in the last few years is cresyl; 75 grains to 35 cubic feet is 

 sufficient to kill all mosquitoes, and in this dilution it is not in- 

 jurious to man or other higher animals. It is not injurious 

 to metals or to household goods. 



