SKIN FILARIA 295 



Prevention. — As the ticks occur upon hosts of many different 

 species, some of them wild animals, and are thus widely- 

 disseminated, complete eradication offers almost insur- 

 mountable difficulties. Dips which kill ordinary ticks, or 

 the Texas fever tick, are worthless for the spinose ear tick. 



THE SCREW FLY. 



The screw fly (Compsomyia macellaria) is a small, bluish- 

 green fly with a brown head and three black longitudinal 

 stripes on the thorax. The female deposits her eggs in 

 wounds, where they hatch in a few hours (larvae, maggots), 

 the maggots burrowing into the tissue, where they remain for 

 a week. They then escape from the wound, reach the ground, 

 pupate, and change to adult flies. In some regions of the 

 South they are very troublesome, infesting the smallest 

 wounds and causing serious losses. 



Treatment. — Pure creolin should be injected into the 

 wound. Fresh wounds can be protected by a tar covering. 



CHICKEN LICE. 



The red chicken louse (Dermanyssus avium) has as its host 

 chickens and other feathered animals. It will, however, 

 attack horses and cattle, producing eczema. In cattle it has 

 been known to enter the ears, causing an external otitis. In 

 rare instances lice penetrate the middle ear, causing symp- 

 toms of cerebral excitement. 



SKIN FILARIA. 



Thread-worms, which are parasitic, invade the skin and 

 subcutaneous tissue of animals. The following varieties are 

 the most common : 



Filaria Irritans. — ^This is a silver-white larva 2 to 3 mm. 

 long, the adult form of which is unknown. It lives in the 

 subcutaneous connective tissue of the horse and is the cause 

 of a skin disease commonly known as "summer sores," or 

 granular dermatitis. The lesion manifests itself first by little 



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