DERMATITIS 467 



than to all other causes combined, therefore, such are consid- 

 ered under parasitic skin diseases. 



Mechanical, — Traumatic causes may be pressure, as lying 

 on hard floor, whipping, bites (flies), running through brush as 

 hunting dogs do, excessive wagging of the tail, friction when 

 bathing by use of stiff brush, and shaking the ears. 



Chemical. — Chemical agents as strong caustic soaps or the 

 too frequent use of ordinary soap; irritating medicinal prepar- 

 ations, as parasiticides improperly applied, or vesicatory 

 agents as mustard. Acids intentionally applied, caustics 

 as use of lime in dusting pens for poultry, and bee or wasp 

 stings are also causes. 



Thermic. — Thermic causes are: Scalding, burning, freezing 

 or exposure to direct sun rays of animals unaccustomed to 

 it after having been sheared. 



Infectious. — Infections of Bacillus necrophorus, especially 

 in suckling young, produce serious necrotic sloughs of the 

 skin. Secondary dermatitis is frequently seen during the 

 course of distemper in dogs. 



Pathology.— The mild, acute form reddens the skin, which 

 becomes sensitive, but is otherwise little changed. The 

 subacute form is shown by a thickening and hardening of 

 the skin. The skin feels rough and fissured. Any serous 

 or hemorrhagic discharge soils the hair and forms crusts. 

 The microscopic examination for parasites is negative and the 

 skin itself shows an increase of connective tissue and general 

 infiltration often to the extent of separation of the layers. 



Symptoms.— Pruritus is usually the first noticeable symp- 

 tom which causes repeated scratching, rubbing on the 

 ground or floor and licking the part. In hunting dogs, 

 especially at the beginning of the season, the skin over the 

 chest and anterior part of limbs, between the toes, and 

 on the end of the tail, will be reddened and moist, often 

 bleeding, while the dog is being used in the field. In dogs 

 and cats following the use of strong or the too frequent use 

 of bath soaps, and in poultry from dusting them in lime, a 

 mild, acute, diffuse dermatitis ensues. Its persistence 

 depends on the continuance of the causes. Sleeping on 

 hard surfaces without bedding causes a chronic local der- 



