URTICARIA : NETTLERASH : DERMATONEUROSES 



Definition. A mild congestion, and exudation into the skin in 

 the form of circumscribed rounded elevations, it may be sym- 

 metrical, often becoming confluent, resembling that caused by 

 stinging with nettles, appearing and disappearing very suddenly 

 excited by local irritation or auto-poisoning, acting on a specially 

 susceptible nervous system and skin. 



Animals susceptible. Urticaria is comparatively common in 

 horses and dogs and somewhat less so in cattle and swine. 



Causes. The fundamental predisposing cause appears to be 

 the individual nervous and cutaneo-vascular susceptibility which 

 resents in this way any irritation to which the skin may be sub- 

 jected. Thus under the same causative factors some animals are 

 severely affected, while others are undisturbed. Like nervous- 

 ness this appears to be at times hereditary, in others it is an 

 individual idiosyncrasy, while in still others it is roused by some 

 weakness or morbid condition of the system, as after some 

 specially debilitating disease, or some abnormal fermentation 

 process in the system. 



On the white and delicate human skin this may be especially 

 marked, the line drawn by the nail or a blunt lead pencil becom- 

 ing the centre of a promptly evolving, spreading eruption, last- 

 ing for a variable time and even appearing again and again. In 

 some animals, and especially in horses, a similar susceptibility is 

 shown, so that the stripe of the whip or friction of the. harness 

 produces such irritation that it is impossible to keep the subject 

 at work. 



It has been especially noted in army horses in low condition, 

 shedding the coat tardily, with coat harsh and dry, skin hide- 

 bound, and in such as become rapidly plethoric on grain feeding or 

 rich spring grass. Again a rainy or stormy season, electric ten- 

 sion, hot moist summers, pregnancy, and lactation seem etiological 

 factors. 



The exciting cause of the affection may be the stings of nettles 

 on the most delicate portions of the skin. In the same connec- 

 tion may be named poison ivy (rhus toxicodendron), poison 

 sumach (rhus venenata), the rhus diversiloba of Pacific Coast, 

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