142 Disturbances of Circulation. 



not so minute that they can be carried from the arteries through 

 the capillaries into the veins, for which reason such emboli from 

 the pulmonary arteries become fixed in their branches, that is, in 

 the lungs ; other types of emboli, however, as minute animal 

 parasites or bacteria, may traverse a capillary area and may there- 

 fore pass from the greater into the lesser circulation and in turn 

 arrive again in the greater. 



In ver}' rare instances in human beings, where there is a patulous 

 foramen ovale, emboli have been encountered in tlie aorta and its branches 

 which did not originate in the left heart or lungs, but which passed 

 directly from the right into the left heart through the patulous opening. 

 When first seen, before the condition of the foramen ovale has been 

 noticed, the existence of such embolism seems inexplicable and confusing, 

 for which reason such an occurrence is spoken of as paradoxical embolism. 

 In addition, it should be mentioned that there is a possibility of retrograde 

 embolism of embolic substances in the veins. This, according to Ribbert, 

 may be explained on the supposition that clots or emboli of any type 

 which happen to lie close to the inner surface of a comparatively large 

 vein are always subject to slight backward repression by recurrent waves 

 of the venous blood (venous pulsation in passive congestion), somewhat 

 as at the shore the surging wave carries back with it a floating log into 

 the sea. If the venous current to the heart be weak^ as in congestive 

 states, it may not carry the embolus forward with it, while the more 

 powerful backward impulse forces it gradually back toward the periphery 

 to the capillaries. [This is well seen sometimes in cases of valvular 

 insufBciency and regurgitation.] 



The results of thrombosis and enibolisni vary with the vascular 

 conditions, the size and nature of the obstructive substance and the 

 relative importance of the afifected organ. In part they are purely 

 mechanical, depending upon the degree of narrowing or obstruction 

 of the lumen occasioned by the process and the consequent dis- 

 turbance of circulation ; in part the results may be specific (pe- 

 culiar), the nature of the thrombus involving some special prop- 

 erties (as pyogenic or putrefactive agencies, or tumor forming 

 elements). Thrombosis of arteries occasions primarily an anaemia 

 of the organ or area supplied by the artery afifected. This anrcmia 

 in vital organs like the brain or heart or lungs necessarily imme- 

 diately induces disturbances of function dangerous to life itself 

 (fainting, cessation of cardiac action, phenomena of asphyxia), if 

 an important artery be involved and quick compensation by anasto- 

 motic blood supply is impossible. In case, however, branches of 

 the occluded or obstructed artery are so connected with other 

 adjacent arteries that a sufficient amount of blood is supplied to 



