EXTERNAL PARASITES 



79 



siticide, that although paris green in solution is a violent poison 

 because of its arsenic content and although tobacco leaves contain 

 nicotine which, when extracted is a parasiticide, yet these agents 

 in their dry state do not destroy mites. 



Naphthalene or powdered moth balls, on account of its vola- 

 tile substances emitted, killed all mites in forty-five minutes. 



Insect powder containing gasoline and crude carbolic acid, on 

 account of the volatile substances given off, killed all mites in one 

 minute. 



In duplicate tests solutions sufficiently concentrated killed in the 

 following length of time: Crude carbolic acid, twenty seconds; 

 five per cent carbolic acid, one minute; one per cent naphthalene in 

 kerosene, thirty seconds; one per cent kreso dip, ten minutes, and 

 two per cent, in four minutes; ten per cent formaldehyd, in ten 

 minutes. Formaldehyd is a slow parasiticide and must be in quite 

 strong solution. Its gas does not destroy flies. Free nicotine in 

 % per cent kills lice in 30 seconds. 



In order that parasiticides be effective in the destruction of the 

 mite they must either be in solution or be capable of giving off 

 volatile substances which in themselves are destructive. 



Dermanyssus Gallinae-Dermanyssus Avium 

 Description. — By referring to Fig. 31 it will be seen that the 

 body of this parasite, commonly known as the mite chigger, differs 

 from the Trombidium holosericeum in that it is ovopyriform in 

 shape instead of oval. The diameter of the posterior third is 

 greater than that of the anterior third. The abdomen and legs 

 are provided with rath- 

 er short bristles. Its 

 mouth parts are conical 

 in shape and arranged 

 for injuring the skin 

 and sucking blood. The 

 color varies according to 

 the amount of blood con- 

 tained within the intes- 

 tinal tract, varying from 

 yellow to a yellowish- 

 red. The free extremity 

 of the legs is provided 

 with an apparatus which 

 enables them to hold on 

 or cling to objects and 

 to move about rapidly. 



Life History. — The fe- 

 male, like the female of 

 the preceding genus, lays 

 her eggs in the cracks 

 and crevices and filth of 

 the floors and nests, 

 where they hatch out in 

 a few days, if the temperature be favorable, 

 asexual larva goes through several moults 

 the adult, sexual, eight-legged parasite. 



Symptoms of Dermanyssus Infestation. — This parasite lives 

 in the poultry houses and dove-cotes, hiding' in the straw of 

 nests, cracks and crevices of the roosts, and otlier x)laces of 



Fig. 31. Dermanyssus Gali.inae. 

 a, conical-shaped rostrum; b, palpus. 



The young, six-legged 

 finally maturing into 



