THE ORGANS OF SPECIAL SENSE. 



231 



scratched with the finger-nail evidently enjoys it. He 

 may be covered with sores from the wounds he has in- 

 flicted on himself when attempting to remove the irritation. 

 Examination of the skin will show red puncta or circum- 

 scribed inflammations, each of which developes into a 

 vesicle in the majority of cases and bursts, giving exit to 

 a sero-purulent discharge, which, mixed with epithelial 

 scales, forms scurfs and scabs on the skin of the affected 

 parts. The hair is soon shed, except that here and there 

 one persists obstinately among the disease crusts. As 

 the disease progresses more skin becomes involved, and 



FlO. 69. — Sarcoptes canis (Geelach). 



that which was first affected becomes hypertrophied, thick, 

 dry, scaby, and corrugated or covered with open sores 

 from the animal biting and tearing himself. Chronic 

 mange causes an anaemic and debilitated state of the 

 animal, and he loses his spirits and value for sport ; he is 

 no longer keen in the field, and his powers of scent notably 

 fail. It is observed by Nunn that the rapid spread of 

 inange over the surface of the body is due to the fact that 

 both bedding and claws convey the parasites. Symbiotes 

 has been found on the dog, but sarcoptes is the general 



