270 DISEASES OF THE SKIN 



TICKS. IXODOIDEA. 



Definition. — Ticks are skin parasites which, however, do 

 not remain parasitic throughout life. The females especially 

 attach themselves to the skin into which they bore. The most 

 important tick is the Texas cattle tick (Margaropus annu- 

 latus) which transmits the germ of Texas fever. While 

 common on cattle in the Southern States it is only an occa- 

 sional visitor in the North, where it is unable to withstand 

 the cold winter. Ixodes reduvius, which is parasitic on sheep 

 and cattle, is not uncommon. The same treatment recom- 

 mended for lice will destroy ticks. (For eradication of the 

 Texas fever tick see Texas Fever.) 



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 gallinae) 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 : 



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