36 BOVINE PATHOLOGY. 



action of the hearty or from a depraved condition of the 

 blood. 



Mechanical Congestion depends upon impediment to 

 return of blood from a part in consequence of pressure on 

 the veins ; it generally assumes the passive character. In 

 active congestion there is swelling, pain, redness, and 

 heat, with an exaltation rather than a perversion of func- 

 tion, but practically it is extremely diflficult to distinguish 

 from inflammation upon which it verges. Passive con- 

 gestion is indicated by swelling due to serous extra- 

 vasation, coldness and deficient vitality of the part, which 

 has a dark blue colour. The swelling is influenced by 

 position of the patient, for it is caused by a watery fluid 

 devoid of plastic elements. Such swellings may dis- 

 appear very rapidly and occur in pendulous positions. 

 Congestion terminates either in inflammation or resolu- 

 tion, and may persist for a long time, giving rise to 

 ExTEAVASATiONS, either serous or sanguineous, or mixed 

 (sero-sanguineous) . 



Seeous Exteavasation may occur either on a serous or 

 mucous surface, or into intercellular spaces. It may be seen 

 in the early stages of catarrh of various mucous membranes, 

 and, mingling with mucus, constitutes the discharge of the 

 early stages of inflammations of those structures. When 

 serum is extravasated into a serous cavity as a result of 

 congestion, it is a salutary relief to the diseased parts, and 

 the liquid can be readily returned into the blood, for the 

 serous cavities are only large dilatations of lymph-vessels. 

 Intercellular collections of serum are similar in their 

 pathological importance. Sometimes, however, accumu- 

 lations of serous or sero-sanguineous fluid appear on the 

 surface of the body as a result of injury ; the surrounding 

 areolar tissue becomes condensed and retains the fluid. 

 Incision into these " serous abscesses " is sometimes 

 necessary. 



Sanguineous extravasation is known as H^morehage. 

 It depends either upon a depraved state of the blood, or 

 on a giving way of the walls of vessels. Not only in the 

 latter case is unaltered blood displaced, but it is allowed 



