Psoroptic Acariasis in Sheep. i8i 



pasturages are among the most prolific causes, as the mingling of 

 flocks, diseased and healthy, their successive pasturing and rest- 

 ing on the same ground, and their use of common objects for 

 rubbing ensure the spread of the psoroptes. This explains the 

 great prevalence of the disease in the unfenced common pastu- 

 rages of central Europe and Asia, of Syria, North and South 

 Africa, of Australia, Argentina, Mexico, and our Western Plains, 

 also, in the early days, in Iowa and elsewhere before th€ land was 

 enclosed. Traveling infested flocks by road comes under the 

 same category. So the modern methods of transit by rail and 

 boat, the concentration of the parasite in the lines of travel and 

 its diffusion to each successive shipment becomes most injurious. 

 The roads, loading yards and banks, chutes, cars, litter, manure, 

 feeding yards, stock yards, alleyways, sheephouses and stock 

 trucks become infested in turn, and each remains for two weeks 

 or more a centre of infection. A single infested flock can thus 

 establish a long chain of infested centres, each of which becomes 

 an active source for the diffusion of the disease. The constant 

 succession of ovine shipment furnishes daily fuel for the flame, so 

 that once started these disease-foci are likely to be permanent 

 sources of trouble. Show-rings and pens hold a very secondary 

 place, as unless newly infested, scabby sheep are rarely in condi- 

 tion for exhibition. Again, an animal only just infested, with 

 its paucity of acari, is immeasurably less likely to transmit the 

 parasite, than is one far gone with the disease, swarming with 

 acari and with the infested portions of the skin stripped of their 

 wool. 



Symptoms. The affected sheep attracts attention by the 

 rough state of its fleece at the affected part, the wool being flat- 

 tened or ragged, with white tufts rubbed out or pulled out by the 

 teeth. It shakes its tail, rubs its body, scratches with its hind 

 feet, and tears with its teeth in a way to show intolerable pruritus. 

 If the affected parts are rubbed with the hand the patient shows 

 its enjoyment by the scratching movements of the hind limbs, 

 the trembling and nibbling with the lips, and movements of the 

 head and body as if rubbing. The itching is encreased by driv- 

 ing or by crowding together so as to heat the sheep and induce 

 oerspiration. The skin of the affected part is covered with yel- 

 lowish papules of varying size, and a marked accumulation of 



