STRUCTURAL CHANGES DUE TO DAMAGE. 297 



the zone of inflammation separating it from the living tissues is 

 called the line or plane of demarcation. (For a fuller explanation 

 of the process of demarcation and of the tissue-changes that lead 

 to encapsulation, the student is referred to the article on inflamma- 

 tion.) 



II. INFLAMMATION. 



It is difficult to frame an accurate definition of inflammation, for 

 the reason that the term includes a number of different conceptions 

 that cannot be readily expressed in concise form. In general, it 

 may be stated that inflammation is a process of repair following a 

 limited damage to the tissues. The injurious agent acting upon a 

 part must inflict a certain amount of damage in order to bring 

 about inflammation : if its action be slight, it will cause only an 

 evanescent irritation which does not pass into inflammation ; if, 

 on the other hand, its action be severe, it occasions necrosis or 

 degenerative changes at the point of its application, and only in 

 remoter parts of the tissue, where its action is moderate, will 

 inflammatory changes be manifested. The nature of the damaging 

 cause and that of the tissues affected both influence the character of 

 the inflammatory process. It therefore manifests many variations 

 under different circumstances, and in order to understand the 

 underlying principles of the process it will be best to select some 

 particular example for a somewhat close study, and then to consider 

 some of the circumstances that modify the phenomena presented by 

 that example. A severe burn, the effects of which extend deeply 

 enough to destroy a part of the true skin, will serve this purpose, as 

 affording an example of acute inflammation of a vascularized part 

 following a cause that has acted for only a short time and has then 

 been removed. 



In considering this example we must distinguish between those 

 destructive effects that are due to the damaging cause, and the 

 reparative processes that follow in the tissue-elements that have 

 been less seriously affected. It will make the example clearer if 

 we also separately consider the phenomena presented by the vascular 

 system from those taking place in the fixed tissues of the part 

 exclusive of the bloodvessels. 



Those tissues which have come into the closest contact with the 

 source of heat will have been quickly killed and, perhaps, charred. 

 Beyond this point of complete destruction the tissues may be roughly 



