620 SCABIES — SCAB — MANGE. 



Tliey soon become more numerous and even confluent, break and 

 discharge, become converted into pustules, and cause the formation 

 of crusts. In a few days the diseased points are covered with a 

 squamous, yellowish, sticky covering, under which the psoroptes lie 

 hidden and which affords them nourishment. 



The crusts steadily grow thicker and lift the individual fibres of 

 wool, tearing them from their follicles, so that patches of skin become 

 bare. The patches thus formed increase in diameter, for the acari 

 leave the centre, where crust-formation is replaced by abundant de- 

 squamation of the epidermis. The sldn is thickened, assumes the 

 character of parchment, and in old-standing cases becomes wrinkled. 



The disease alwaj's commences along the back, withers, loins, and 

 the upper part of the quarters. Thence it spreads to the flanks and 

 sides of the chest. The psoroptes are almost exclusively confined to 

 recently affected points on the edges of the scabby patches. They 

 are visible to the naked eye, and appear as little whitish-brown 

 points. 



Scab is specially liable to attack a flock containing lambs and 

 yearling sheep, whose skin is thin, fine and supple, and therefore 

 more susceptible to their attacks. If a portion of a scabby flock be 

 shorn, the shorn animals will probably recover on account of the 

 psoroptes transferring themselves to the animals with long fleeces. 



The diagnosis is easy. Psoroptic mange cannot be mistaken for 

 sarcoptic mange, on account of the difl'erent points afi'ected. 



Psoroptic mange only attacks regions covered by wool, and sarcoptic 

 mange those free of wool. A microscopical examination of acari re- 

 moved from the diseased animals will, however, immediately remove 

 all doubt. 



Nor can the disease be confounded with phthiriasis, the tricho- 

 dectes being immediately distinguished from the psoroptes by their 

 greater size and the shape of their head. Moreover, they are usually 

 to be found on the front portions of the shoulders. 



It is more likely to be mistaken for another disease, termed by 

 some writers seborrhcea and studied and described by Delafond under 

 the name of sebaceous folliculitis. This disease appears mostly in 

 autumn, and attacks animals much exposed to the weather and on 

 moist, cold soils. It begins with very violent pruritus, followed by 

 biting and loss of portions of the fleece. The skin is red, inflamed 

 and painful, and the wounds are covered with large quantities of 

 yellowish acid discharge of a sticky and offensive nature. The treat- 

 ment of this disease consists in placing the sheep in clean, dry, well- 

 ventilated sheds. Piecovery is assisted by clipping and the application 

 of some emollient dressing to the diseased parts. 



