CHAPTER XV. 



parasitic Diseases of the Skin. 



While the diseases of this particular class are not so 

 dangerous to the animal's existence as those occurring from in- 

 ternal parasites, yet we must place great importance on disease? 

 of this nature, as to one of them at least, viz., scabies, the greatest 

 loss of the wool-grower is directly attributable. The yearly 

 shrinkage of the wool crop due to its attacks amounting througli- 

 out the world to millions of dollars. All diseases of the skin 

 tend to produce bodily discomfort, the sheep after feeding in- 

 stead of being able to rest quietly, is called upon to resist the at- 

 tacks of pests, the excessive itching always present in these com- 

 plaints caiTsing the animal to rub itself violently and pull the 

 fleece from the diseased surfaces with its mouth. Animals suffer- 

 ing from these attacks do not fatten readily. Should they be 

 neglected, no treatment being used, the diseases become vii'ulent, 

 the animal perceptibly loses flesh, and is virtually eaten alive by 

 ever-increasing multitudes of parasites. 



Scabies, Scab. 



Is a disease due to the presence of an animal parasite, which 

 exists on the effusion arising from the irritation to the tissue- 

 caused by its presence. Of the scab insect infesting sheep we 

 find three kinds, namelv, the sarcoptes ovis, which burrow in 

 the skin; the dermatodectes, also called the psoroptes communis, 

 the cause of common ?cab, which simply bite and hold on to the 

 skin, and which is the parasite we shall mostly have to deal with 

 in tills chapter, and thirdly the symbiotes, or chorioptes ovis, the 



