INFLAMMATION. 115 



extravasated red blood cells aud fibrin and a disteution of the tissue 

 spaces with fluid still further characterize the process as exudative in- 

 flammation. 



It was observed in the exposed mesentery or bladder of the frog that 

 the leucocytes, once outside the vessels, wandered off in various direc- 

 tions in the tissues, some to the surface, some to the lymph- vessels, and 

 some far from the veins or capillaries from which they emerged. Not so 

 here. The extravascular leucocytes gather close in the border zone of 

 the necrotic area or enter it. And we may usually see in the outer parts 

 of such an area of dead tissue scattered leucocytes which are themselves 

 undergoing changes indicating the death of the cell. The changes which 

 have just been described as the result of experiment in the animal are 

 practically identical with those occurring in man as the result of acci- 

 dental inoculation. 



If the process continue, one may find on later examination that the 

 dead-tissue mass has softened, the bacteria are scattered, and the whole 

 central portion may be occupied-by a grayish or yellowish grumous or 

 fluid mass of dead cells, ceH^^tran^sfaibuminous and fatty granules, 

 bacteria and leucocytes in various stages of necrosis and disintegration. 



Such a localized result of exudative inflammation with death and dis- 

 integration of tissue is called an abscess ; the material which it contains 

 is called pus. 1 



The changes by which, if the animal survive the formation of abscess, 

 the active processes are brought to a standstill and repair is effected, we 

 need not now follow. But it concerns us here to appreciate that this is 

 a type of one of the most important phases of the inflammatory process ; 

 a phase in which a poison produced in the body by the metabolism of 

 micro-organisms incites a complex train of active and passive tissue 

 changes. 



In our study of illustrative phases of inflammation we now turn to 

 the processes by which repair of injured tissues, after more or less in- 

 volvement in the inflammatory phenomena, are brought about. 



Resolution in Inflammation Phagocytes. In many cases of exudative 

 inflammation, after the subsidence of the active changes in the blood- 

 vessels, the exudates are entirely absorbed, and the tissue returns to its 

 normal condition ; this is called resolution. Under certain conditions, on 

 the other hand for example, in the case of a wound with loss of sub- 

 stance, or in an acute exudative inflammation of a serous membrane 

 in which the surface is deprived of its normal mesothelial 2 covering, or 

 in the healing of an abscess new tissues may be produced through the 

 agency of old cells or of new cells formed in the inflammatory process. 



1 For a more detailed consideration of suppuration and the characters of pus see p. 

 175 et seq. 



s The morphological resemblance of the flat cells covering the surfaces of the great 

 serous cavities peritoneal, pleural, and pericardial to the endothelium of the blood 

 and lymph-vessels has led to their being also called endothelium. But their genesis as 

 well as certain physiological capacities which they still retain, render more fitting the 

 name mesotheliiim. See reference to Mi not in footnote on p. 325. 



