ITCH MITES. 307 



CASE and lose their brilliancy: they become white and atrophied 

 as if there were some perversion of the secretion of the skin 

 of the bulb. At the point where the feather detaches itself 

 from the skin, there is found a mass of epidermic matter in a bed 

 of the thickness of some miUimetres, and all around are lines or 

 burrows formed by the raising of the skin. 



As the malady proceeds, the feathers of the head and upper 

 part of the body become atrophied ; their free extremity bends, 

 twists, and rolls upon itself, and ends by disappearing in the 

 midst of the epidermal products accumulated at the base of 

 the quill. The head and neck of the fowl have at that period a 

 very peculiar aspect; they are despoiled of all the feathers that 

 decorate them in their normal state. The comb is brown with a 

 rugged surface, drawn back upon itself, broad at its base and 

 spotted with whitish mealy patches. On various parts crusts, of 

 some lines in thickness, appear, which, when detached, leave a 

 slightly scaly surface, which recalls to mind the disease named 

 phthiriasis. The complaint does not always begin on the head. 

 It sometimes makes its first approaches on the feet. Similar 

 symptoms occur there, but they proceed more slowly, but by-and- 

 by the scales on the feet and legs begin to come off, and a crust 

 forms upon them, more especially between the toes. Sometimes 

 it envelops the whole of the foot and tibia, forming a crust a third 

 of an inch in thickness. Bits as large as a hazel nut, or a walnut, 

 may be broken off. This [affection has much analogy with the 

 Norwegian itch above described. It can be communicated both 

 to man and to the horse. 



Genus Psoroptes {Gerv.). (Dermatodectes, Gerlach; 

 Dermatokoptes, FiLrst.) 



Palpi soldered to the mandibles, of which there is only one 

 pair, which is adapted for piercing and not chelate ; stem of the 

 suckers or ambulacra three jointed. 



u 2 



