262 TEXT-BOOK OF PHYSIOLOGY. 



or thrombus is not a true coagulum as ordinarily understood, but 

 rather a conglutination of blood-elements. Whenever the integrity 

 of the internal wall of the vessel is impaired by disease or by the in- 

 troduction of foreign bodies, there is primarily a deposition and 

 accumulation of blood-plaques at the injured area or on the foreign 

 body which constitutes to a large extent the mass of the thrombus 

 which at once forms. The thrombi which form on the surface of 

 atheromatous ulcers, on the valves of the heart, and in the veins in 

 consequence of diseased states, on threads or needles passed through 

 the vessels, at the orifices of torn blood-vessels, consist largely of 

 blood-plaques. A thrombus so formed may contain a number of 

 delicate fibrin threads, which, however, present a different appear- 

 ance from the fibrin of the extra- vascular clot. In the thrombi which 

 form around foreign bodies there is always a larger quantity of fibrin 

 than in those originating from causes wholly within the vessel. 



