GENERAL PATHOLOGY. 25 



Organization is commonest in arteries, while softening is 

 chiefly met with in the veins. 



RESULTS OF THROMBOSIS.— The coats of the vessels 

 are altered, and unless collateral circulation be established, 

 thrombosis of an artery will lead to death of the parts sup- 

 plied. Thrombosis of an important vein will cause painful 

 swelling ; if continued long, nutritive changes in the parts 

 it drains, and mechanical hypersemia, will follow. 



A fragment of the thrombus maj^ be washed away by 

 the blood current, thus leading to embolism. 



EMBOLISM. 



Embolism is the impaction of solid substances circu- 

 lating in the blood-vessels which are too small to allow them 

 to pass. These solid substances, which vary much in their 

 nature, are termed emboli. The most frequent causes of 

 embolism are detached fragments of thrombi in the veins, 

 vegetations, and morbid debris from the heart, portions of 

 new growths and parasites. 



An embolus which arises in the systemic veins will pro- 

 bably be arrested in one of the small branches of the pul- 

 monary artery ; while those arising from the pulmonary 

 veins, or heart, will be lodged in the systemic arteries, and 

 those from the radicles of the portal vein in the liver. 



Thus the seat of embolism is either in the arteries or in 

 the hepatic branches of the portal vein. 



The arrest of the embolus, and the consequent obstruction, 

 are followed by the formation of secondary thrombi behind 

 and in front of it. The secondary thrombi extend as far 

 as the entrance of the iirst large collateral vessels. 



Emboli may in rare cases be absorbed. When derived 

 from thrombi they may organize or soften. 



RESULTS OF EMBOLISM.— An embolus cuts off the 

 supply of blood from the area to which the vessel is dis- 



