330 THE DOG IN DISEASE. 



The external sources of irritation may be parasites — 

 vegetable or animal — or bedding that is old, damp, satu- 

 rated with exhalations from the animal's body, or possibly 

 urine or f geces. 



The above may be direct exciting causes, but such are 

 not essential to skin disease. Certain conditions of body 

 predispose, and these arise from excessive or otherwise 

 improper feeding, lack of exercise, or starvation, and gen- 

 eral inattention to sanitary surroundings. 



It is always to be remembered that pure-bred dogs are 

 disordered by an environment in wiiich a mongrel might 

 do fairly well. So common a cause is overfeeding, that a 

 certain form of inflammation of the skin has been called 

 " surfeit " or blotch. 



Of course the presence of parasites, by the itching some 

 of them cause, leads the subject to scratch so much that 

 this of itself suffices to explain the inflammation, altogether 

 apart from their own biting and burrowing. 



Pathological Condition and Symptoms. — As in other 

 inflammations, there is heat, redness, pain or tenderness, 

 and swelling ; but these are present in very varying de- 

 grees in different cases. Perhaps the most typical form 

 of inflammation is that known as eczema. A localized, 

 swollen, more or less red, tender area, known as a pimple 

 {papule), appears, which soon has its epithelial covering 

 raised by exudation from the blood-vessels and becomes 

 a vesicle, which may be filled with a clear, a turbid, or 

 a purulent fluid. In the latter case it constitutes a pus- 

 tule. These sooner or later burst ; the fluid escapes, 

 irritates the adjoining skin, and dries into more or less 

 well-defined scahs. If the animal scratches, these may 



