744 LOCAL CONGESTIVE AND INFLAMMATORY DISEASES. 



Urticaria — Syn. Nettle Rash. 



Definition. — An eruption over irrefjularhj distributed, fre- 

 quently sy7)iinetrical jjortions of skin ; of slightly elevated, ovcd, 

 or roxmdish patches ; soft, but possessed of a moderate amouMt 

 of resistance to the touch, and extremely evanescent 



Pathology, a. Nature. — This is an extremely interesting 

 disease ; and in the horse, as well as in cattle, it may appear in 

 almost any part of the body, being, however, less frequently 

 seen on the limbs, seeming to have a partiality for the head, 

 neck, and upper parts of the trunk. It appears without pre- 

 monitory symptoms, and may or may not be accompanied 

 with fever and general disturbance. When appearing in certain 

 parts of the body special symptoms attend such developments. 



b. Causation. — The agencies and influences operating in the 

 production of this condition are, like those related to several 

 other cutaneous disorders, various ; but probably all turn upon 

 the disturbance of nutrition in the parts invaded, such as — 



(1) Local irritation to a naturally hypersensitive skin ; 



(2) Reflected irritation from deranged digestive organs; (3) Effete 

 material circulating in the blood — this may be regarded as only 

 another form of direct local irritation. 



The exact rationale of the production of the immediate 

 manifestation of the disturbance is not without difHculty of 

 explanation. The anatomical features point to the infiltration 

 of the superficial part of the papillary layer of the corium, and 

 of the layers of the epidermis ; while the suddenness of the 

 appearance of the swellings, and their equally sudden dis- 

 appearance, and the absence of sequela?, seem to indicate some 

 other cause in operation than impurity of blood. Certain 

 atmospheric and meteorological disturbances have been supposed 

 to be in operation for the production of these phenomena, 

 while there is not wanting evidence to favour the idea of its 

 neurotic origin and intimate connection with disturbed vaso- 

 motor power. It does not, in any animal, seem to be of a 

 catching nature, and inoculation with the blood has failed to 

 produce it. 



Symptoms. — These are distinctive, and not likely to be mis- 

 taken : rapid of development, and scattered over various parts 

 of the body, the wheals or circumscribed swellings resemble 



