136 Disturhances of Circulation. 



The clots appearing at the beginning of thrombosis are known 

 as primary (autochthonous) thrombi; the coagula subsequently 

 deposited upon them as secondary or consecutive thrombi. The 

 former are more or less firmly attached to the vessel wall {parietal 

 thrombi) ; the latter usually lie free in the lumen as cylindrical 

 plugs with conical or rounded ends. The thrombus increases prin- 

 cipally in the direction of the blood stream, in the arteries toward 

 the periphery of the circulation, in the vei,ns centripetally. The 

 length may be quite considerable, as in those extending from the 

 veins in the neck down into the heart, or from the aorta at the 

 level of the renal artery down into the arteries of the popliteal space 

 and leg with or without (discontinuous) continuity. The thickness 

 depends upon the calibre of the blood vessel ; parietal clots are at 

 first flat, marked with wavy ridges, villous, or in the pockets of the 

 valves of the veins may form smoothl}' rounded plugs (zalviilar 

 thrombi) ; with growth the thrombus ma}- cause complete occlusion 

 of the vascular lumen (total occluding thrombi). In arteries 

 thrombi are usually smaller than the calibre of the relaxed vessel, 

 being compressed by the contraction of the i)ulsating vessel wall. 

 In aneurisms and in the cardiac chambers there occur huge irregular 

 nodulated thrombi, sometimes are large as the fist. Thrombi in 

 the course of time undergo a number of changes (metamorphoses) 

 as well might be supposed. They are but dead masses made up of 

 coagulated and necrotic elements and may shrink, becoming firmer, 

 drier and smaller; such changes depending upon changes in the 

 structure with homogenization of the fibrin and plaques and upon 

 pressure exerted by the walls of the vessels. In clots which have 

 undergone such changes there may occasionally take place a calcare- 

 ous deposit (vein stones, phleboliths). As a result of such shrink- 

 age the vascular lumen may again become partially permeable to the 

 blood. [The diminution in size of an old clot depends in an im- 

 portant degree upon the shrinkage of its own fibrinous network ; 

 this may be easily noted in the shrinkage which takes place in any 

 clot outside the body, with the separation of the serum originally 

 present in the coagulum, the question of compression by the vessel 

 walls being in such case entirely eliminated.] The most common 

 change consists in a softening of the thrombus, the clot being trans- 

 formed by fatty degeneration of its leucocytes [and liquefaction of 

 any of its elements] into a gray or grayish-red mass of pultaceous 

 consistence somewhat like minced meat. This change may be a 

 favoring circumstance, but is open to serious consequences. In 



