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ARACHNIDA. 273 
covered by them is lightly chagrined and of a brown color, which contrasts with the 
red color of the rest of the comb. Atthat period no lesion of the tissues is observa- 
ble. The malady remains stationary for fifteen days or even a month, at the end of 
which time the base of the comb thickens and becomes darker, and the linear trac- 
ings assume the appearance of true burrows of the itch insect, and at the bottom of 
them the Sarcoptes mutans is to be found. At a later period the feathers of the head 
and about the beak undergo a remarkable change. They turn back, stand on end, 
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 
Fic 164.—Sarcoptes mutans: male and female (copied from Murray’s figures reduced from Robin). 
detaches itself from the skin there is found a mass of epidermic matter in a bed of 
the thickness of some millimeters, 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 
ascaly 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 symp- 
toms occur there, but they proceed more slowly, 
but by and by the scales on the feet and legs F'6- 165.—Sarcoptes mutans: side view 
; (copied from Murray's figure after 
begin to come off, and a crust forms upon them, Robin). : 
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 atfee- 
tion has much analogy with the Norwegian itch above described. It can be com- 
‘municated both to man and the horse. (Murray.) 
4653—No. 5——18 
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