28 INFLAMMATION. 



tlirongli which the blood, diverging from the main stream, and 

 tlien rejoining it, may be continuously propelled : or a delicate 

 threadlike process shoots from a vessel, and becomes connected 

 with corresponding shoots from otlier vessels. These fine pro- 

 cesses widen out, become tubular, and their cavities form canals 

 continuous with those of the parent vessels. When the new 

 blood-vessel has begun to project it sometimes bursts ; the blood- 

 globules that issue from the ruptured pouch collect in an un- 

 certain mass within the tissue like a mere ecchymosis, but before 

 long they manifest a definite direction ; and the cluster bends 

 towards the line in which the new blood-vessel micfht have 

 formed, and opens into a portion of the arch, or into some 

 adjacent vessel. For this mode of formation from vessels the 

 name of channelling seems appropriate, for it appears certain 

 that the blood-globules here make their way in the parenchyma 

 of the tissue unconfined by membranous walls. The new vessels 

 possess a very simple structure, their walls being a thin mem- 

 brane with imbedded nuclei. — (Virchow, Paget.) 



Effusion differs from the so-called exudation of lymph in 

 the fact that it occurs from the surface of serous membranes, 

 blisters on the skin, or in a very loose areolar tissue, where the 

 process of perverted nutrition is of the most rapid kind. 



The fluid found in serous cavities and in serous abscesses 

 partakes of the general characters of the serum of the blood 

 slightly modified, being of a higher specific gravity and con- 

 taining more albumen, with more or less fibrine. Many speci- 

 mens of the effusion found in pleuritis, for example, contain 

 fibrine in an imperfectly developed condition — fibrine which 

 does not coagulate until it is exposed to the atmosphere. 



Now, if the fibrine were transuded through the walls of the 

 vessels, it would in all cases coagulate within the body; but 

 when, owing to the inflammation being near or upon the surface, 

 or in very loose areolar tissue, the transformation of the transuded 

 material takes place rapidly, and hence imperfectly — that is to 

 say, when the fluid sweats through the walls of the cells in 

 an imperfectly developed condition, or, when occurring upon 

 a serous membrane (it is also the case in a mucous membrane), 

 the epithelial scales are rapidly thrown off, along with the fluid 

 they secrete. 



In many effusions we find completely developed fibrine 



