Embolism. 1.^9 



thrombi, no matter whether loosel\- or tirmly attached, may some- 

 times accidentally be torn loose by external force exerted upon the 

 vessel through movements occasioning twisting of the vessels or 

 increase of blood pressure. At the points of branching of the 

 vascular tubes it may happen that a thrombus or embolus may 

 strike upon the dividing angle and here again be broken into frag- 

 ments or may remain fixed at the point of division. It is quite 

 likely that an unusually long, flexible and tough thrombus may so 

 lodge at these places of division as to extend into both branches 

 of the vessel, riding as if in a saddle (riding embolus). A long 

 cvlindrical. flexible thrombus may, moreover, be thrown into folds, 

 twisted in serpentine fashion and compressed into a mass by the 

 force of the blood stream. 



Although an embolus displaced from its original site is forced 

 into a relatively narrow portion of the vessel, it does not neces- 

 sarily at once completely occlude the lumen, since as a broken 

 fragment of a thrombus it need not retain the cylindrical shape 

 of the vascular tube, but may well be of irregular and angular 

 outline. Such emboli, particularly when of the riding type, are 

 apt to leave room free about them for the passage of blood. Cyl- 

 indrical or round emboli are comparatively easily forced into the 

 vascular lumen and give rise to complete obstruction. An embolus 

 which has become lodged tends to further enlargement, either by 

 the massive coagulation of the stagnant column of blood adjacent 

 or by the deposition of thrombotic layers. Sooner or later this 

 leads to complete obstruction of the vessel. In these cases it is 

 often difficult to determine whether there was primary thrombosis 

 or whether an embolism formed the nucleus of the blood clot, 

 which, from the formation of new layers, comes to completely fill 

 out the lumen of the vessel, and the original embolus may, more- 

 over, have been very small, and entirely hidden by the further 

 depositions. 



The course traversed by an embolus is determined by cir- 

 culatory circumstances. An embolus carried from the veins must 

 always pass into the right heart and thence into the pulmonary 

 arteries; it may, however, adhere to the auriculo-vcntricular valve 

 leaflets in the heart. Its convection to the heart is easy, the veins 

 becoming wider and wider from the periphery centrally to the 

 venje cavse. If therefore a fragment become loosened from a 

 thrombus in veins of the foot, thymid. uterus or liver it would 

 be swept by a continually widening current to the heart. Commg 



