740 LOCAL CONGESTIVE AND INFLAMMATORY DISEASES. 



had they not. aheady received a position and designation as 

 distinct diseases. 



The forms of vascular disturbance of the erythematous 

 type which are seated in the vessels of the papillary layer of 

 the dermis, or alone in the capillaries of the hair-follicles and 

 glandular structures, are in the horse chiefly exhibited as 

 Erythema and Urticaria. Owing to the pigmented condition 

 of the horse's skin, change of colour is not observed, while the 

 close covering of hair considerably obscures the swelling, which, 

 in some instances, is slight. The course of both these affec- 

 tions is generally acute, or, if chronic, it is by repeated attacks, 

 while the secondary effects are desquamation. 



Erythema. 



Definition. — A condition of vascular turgescence or hy2)€r- 

 cemia, usually occurring in patches more or less extensive, 

 with a certain amount of effusion into the deeper layers of the 

 epidermis. 



General Characters and Form of Development. — It is a non-con- 

 tagious affection, idiopathic or symptomatic, active or passive. 



With our patients its usual form is idiopathic and active. 

 The patches are slightly elevated, sometimes with a well- 

 defined margin, at others gradually shading off into the healthy 

 skin, which it has a tendency to invade. These are at first 

 tolerably firm, if not much elevated, but, as they subside, 

 become softer. With its apj^earance in any form there is little 

 general disturbance ; only a trifling amount of itching or 

 exudation, not like eczema. When it declines there may be a 

 greater or less amount of desquamation. In its development 

 several modifications may be noticed, and these have been 

 named sometimes in accordance with their form, and at others 

 from the causes supposed to be operating in their produc- 

 tion. 



Erythema^ trauinaticum vel Paratrimma is the circum- 

 scribed hypersemia, with serous effusion into the skin-tissues, 

 occurring as the result of pressure from badly fitting collars, 

 belts, or saddles. This condition, first showing itself in distinct 

 patches, slightly elevated and tender, may, if the pressure is 

 continued, terminate in more serious changes, as the fonnation 

 of abscesses. 



