142 VETERINARY PATHOLOGY. 



necessary for repair of such an injury is variable according to 

 the extent of the injury and the readiness of response of the 

 tissue. 



In vascular tissue the following reaction occurs. An asep- 

 tic cutaneous incision unites almost immediately if the wound 

 margins are placed and maintained in exact apposition. The 

 tumefaction is slight because of the limited extravasate from 

 the severed vessels. There is a slight exudate which coagu- 

 lates and cements the margins or lips of the wound. In a 

 microscopic section through such a wound some cells are found 

 destroyed and others injured. The cells bordering such an in- 

 jury sometimes increase in size to such an extent that they 

 project into the cement between the two incised surfaces. Wan- 

 dering cells and leucocytes in varying numbers appear through- 

 out the entire injured area. The cement (exudate) and the de- 

 generated and necrotic marginal cells are later absorbed. The 

 cells bordering the incision multiply by direct cell division, the 

 newly formed cells replacing those destroyed. New capillaries 

 extend through the newly formed tissue. Finally the leucocytes 

 emigrate and disappear from the injured area. 



In a more extensive injury, such as a gaping wound that 

 later becomes infected, a more complex reaction is observed. 

 The following changes take place during the first twenty-four 

 hours after an injury of this nature is inflicted. There is hem- 

 orrhage, the extent of which depends upon the size of the ves- 

 sels severed and the gaping of the wound. The extravasated 

 blood accumulates in the wound and also infiltrates the ad- 

 jacent tissues. The injury (irritation) causes h3'peremia, es- 

 pecially of the arterioles, resulting in engorgement of the capil- 

 laries. From the engorged and dilated capillaries there is 

 marked exudation. The exudate escapes upon the wound sur- 

 face and infiltrates the tissues of the injured area. The ac- 

 cumulation of the hemorrhagic extravasate and the inflam- 

 matory exudate plus the increased size of the vessels (hyper- 

 emia) tumefies rir swells the injured area. There is an ac- 

 cumulation of mononuclear leucocvtes or wandering connec- 

 tive tissue cells in the injured tissue and an immigration of 

 polymorphonuclear leucocytes. Many cells are destroved out- 

 right by the injury or by the action of infectious bacteria. 

 Those cells bordering the destroyed cells are injured and be- 

 come tumefied and may later undergo necrosis. The cells, es- 

 pecially the connective tissue cells located peripherally to the 

 injured cells, become enlarged and multiply by indirect cell di- 

 vision. The injured cells are repaired and the newly formed 



