276 DISEASES OF THE SKIN 



Similar nodes may form on the mucous membranes of the 

 nose and larynx: This complication may lead to cough, 

 dyspnea, and edema of the glottis. In the vagina and rectum 

 they may induce swelling and occasionally prolapsus recti. 

 Urticaria may also involve the mouth and conjunctiva. Con- 

 comitant with the eruption there may be symptoms of general 

 disturbance, such as fevei- and loss of appetite. 



Course. — Urticaria usually disappears in from one to two 

 days. In swine it may take from four to six days. In rare 

 cases so much serum has accumulated between the corium and 

 Malpighian layer that vesicles appear and the healing, which 

 takes place under scab formation, is prolonged. Chronic 

 cases have been noted, occurring with frequent relapses and 

 causing the condition to last several weeks or months. Very 

 rarely death results from edema of the glottis. 



Treatment. — ^As urticaria usually heals spontaneously, 

 treatment is rarely necessary. The animal should be placed 

 on short rations and a good laxative given. Local applica- 

 tions to the skin are rarely indicated. 



ALOPECIA. 



Definition. — By alopecia is meant a falling out of the hairs 

 without apparent skin lesion, and not due to parasites. 

 Clinically two forms of alopecia are distinguished : (a) Gen- 

 eral alopecia (A. symptomatica), and (6) local alopecia 

 (A. areata). 



Etiology. — (a) General alopecia, which consists in the hair 

 falling out over the whole body, seems to be due to some 

 disturbance in the nutrition of the skin with atrophy of the 

 hair roots. It is most frequently seen to follow infectious 

 diseases, such as influenza, purpura, or tetanus. Poisoning 

 with mercury and lead and with certain foodstuffs (potatoes) 

 in horses is a cause. Obesity is also accused. 



(b) Local alopecia is probably due to a trophic neurosis. 



Symptoms. — General alopecia usually affects the whole 

 body, the mane and tail being the last to fall out. The hair- 

 coat gradually grows thinner and thinner until it disappears 

 except in a few places, where it is usually retained. The 



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