THEOMBOSIS. 231 



have become cloudy, so that they can hardly be distinguished 

 from the white corpuscles proper ; their stroma now becomes 

 dissolved as well, giving the fluid products of softening a 

 mucoid, often stringy consistency. The colourless cells also 

 break up into minute granules. The resulting liquid contains 

 therefore as a rule nothing but granular debris and oil-globules ; 

 and to these it owes its yellowish-grey puriform aspect; true 

 pus-corpuscles (even if we include the colourless corpuscles of 

 the blood under this name) occur only in very small number, 

 and there is no question of any proliferation of corpuscular 

 elements ; so that to call the softening of thrombi a suppuration, 

 though it does convey some idea of the naked-eye appearances^ 

 fails entirely to hit the essential nature of the process. 



§ 196. The softening of thrombi is in more than one respect 

 dangerous. First among j)ossible mishaps, we have the chance 

 that wherever the clot is freely exposed to the blood-current, bits 

 of it may be detached and carried away. Should this come 

 about, the fragments may be carried with the stream (a) from 

 the radicles of the vena cava through the right heart into the 

 lungs ; Q)) from the radicles of the pulmonary veins through the 

 left heart into various organs of the body ; (c) from the radicles 

 of the portal vein into the liver. The distance to which they 

 penetrate into the circulatory tract which they have entered 

 depends upon their size. It is obvious that only particles no 

 bigger than blood-corpuscles can travel without hindrance 

 throughout the whole circulatory system. Any particle of 

 larger size than this must be stopped somewhere or other, 

 blocking the vessel in which it is arrested (Embolism). 



Much might be said about the course emboli prefer to take. 

 In the lungs they most frequently select those long, straight 

 branches of the pulmonary artery which run along the inner 

 surface of the middle and lower lobes to their edges and the 

 neighbouring parts of their external surface. In the systemic 

 circulation the larger emboli most frequently select the popliteal 

 and Sylvian arteries. The embolus in these cases appears to 

 follow the most direct route, that in which there are fewest 

 turnings. It seems to happen not unfrequently that an embolus 

 is driven against the projecting angle between two bifurcating 

 divisions of an artery, and there broken up into smaller frag- 

 ments like a floe of ice against the piles of an ice-guai'd. These 



