i6o OPERATIVE TECHNIQUE. 



divided into two classes — the red and the white. Zahn states that 

 white thrombi result from accumulation of white blood -corpuscles in 

 the lumen of the vessel ; others, however, regard white thrombi as being 

 formed b\' " blood-plaques," /. e. small, colourless, discoid elements, the 

 origin and significance of which are still doubtful. These are said to 

 adhere to the injured portion of the intima coat, and finall)' to entirely 

 close the lumen of the vessel. 



Red clots result from coagulation of the blood, but in the living body 

 they occur much less frequently than the white, though they are seen 

 after severe damage to the vessel wall implicating the intima ; they 

 are commonest in infectious diseases. Red clots are, therefore, most 

 commonlv seen in inflammatory diseases of the vessels and in pyaemia. 

 Sometimes white and red clots may be formed simultaneously in the 

 same vessel. 



Ligation of an artery is not always followed by thrombus formation ; 

 should the tunica intima not be gravely damaged or infected, the 

 endothelium proliferates and the walls become adherent. In other 

 cases a white thrombus forms, or if the parts be severely injured or the 

 circulation be gravely impeded a red thrombus may be produced. 



Pathological clotting demands not only the presence of fibrinogen 

 and fibrinoplastic substance but also of fibrin ferment, which is furnished 

 by the injured cells. In this case the essential part is played by the 

 endothelium of the vessel, which, owing to defective circulation, under- 

 goes degenerative changes, and thus brings about clotting. 



The thrombus either become converted into organised connective 

 tissue or it softens and breaks down. The former is the more favour- 

 able development, and consists in the gradual replacement of the 

 thrombus by connective tissue, which usually results from proliferation 

 of the endothelial lining of the vessel. The endothelium is first con- 

 verted into polymorphous " formative cells," which rapidly multiply, 

 extend into the thrombus and replace it, leaving of the original thrombus 

 only a pigment residue (oxy hydrate of iron). From the vasa vasorum 

 new blood-vessels extend into the new tissue,' converting it practically 

 into connective tissue. The thrombus thus plays a passive part, being 

 gradually replaced by fibrous connective tissue. These changes occur 

 with comparative rapidity ; vascular new tissue may be found at the 

 point of ligation eight days after operation ; in three to five weeks the 

 thrombus, which, like a cicatrix, gradually contracts, is entirely organised. 

 Where, however, the intima is extensively diseased, or where general 

 constitutional disturbance exists, the changes proceed more slowly. 

 Sometimes the new^ connective tissue becomes permeated with hollow^ 

 spaces (Rokitansky's sinusiform degeneration), and the lumen of the 

 vessel m.ay thus be again partially restored. Finally, the thrombus may 

 become calcified, so that it resembles a stone. To the occurrence of 

 this change in venous thrombi is due the production of " phleboliths." 



Circulation is usually restored by collateral circulation, the smaller 

 vessels enlarging and conveying the blood by parallel paths. This 

 change also is often very rapidly effected, as shown by Nothnagel's experi- 

 ments on rabbits. Six days after ligation of an important vessel the 

 muscular coats of the dilated collateral vessels were found to be 



