STRUCTURAL CHANGES DUE TO DAMAGE. 329 



monary tissue, and that through this cavity, or within its walls, a 

 pervious vessel of considerable diameter may take its course. After 

 a while the wall of this vessel may become sufficiently destroyed to 

 yield before the pressure of the blood within it ; rupture may then 

 take place, with the effusion of considerable blood, haemoptysis. 

 In many cases, however, such a result is prevented by the forma- 

 tion of a clot (thrombus) within the vessel before erosion of its 

 wall has gone far enough to threaten rupture. 



Thrombosis. This term is applied to the formation of fibrin 

 within the circulatory system during life. It may take place when 



FIG. 290. 



Haemorrhage in the kidney following general infection. (Tizzoni and Giovannini.) The 

 haemorrhage has taken place within the capsule of a Malpighian body and part of the 

 extravasated blood has passed into the corresponding uriniferous tubule. The glomer- 

 ulus has been compressed (to the right), an occurrence which probably checked the 

 haemorrhage. The tissues of the glomerulus and of the neighboring tubules are necrotic. 



the circulation in a particular vessel or in a portion of the heart is 

 sufficiently sluggish to permit leucocytes and, perhaps, blood-plates 

 to collect and remain in one place long enough for their disin- 

 tegration to begin. The elements required for fibrin-formation are 

 then set free and thrombosis results. In this way thrombi may 

 form between the columnse carnese in marantic conditions, behind 

 the curtains of venous valves, or in the lumina of dilated veins 

 within the pelvis. Thrombosis may also occur as the result of a 

 roughening of the intima of a vessel or its mechanical destruction, 

 as in the tying or crushing of a vessel. 



Thrombosis may be the result of disease of the vessel-wall, caused 

 by infection or malnutrition. The affection of the veins known as 

 septic thrombophlebitis may be selected as one of the more impor- 

 tant acute lesions of the vessels. This is caused by an infection of 



