CHANGES IX THE CIRCULATION OF THE BLOOD. 77 



may occur iii its periphery, the blood and involved tissues may undergo 

 degeneration and be absorbed, and finally the seat of the infarction may 

 be indicated only by a mass of cicatricial tissue, which frequently con- 

 tains more or less pigment. 



In another class of cases, instead of an extravasation of blood in the 

 affected region the tissue is simply deprived of nourishment and under- 

 goes necrosis. The affected area is then usually light in color and is 

 called a white infarction. Inflammatory changes may occur in its periph- 

 ery and a new connective-tissue capsule form around it, and the dead 

 mass may thus persist for some time, or be gradually absorbed and re- 

 placed by cicatricial tissue. The scope of this book does not permit us 

 to consider the somewhat complicated and often obscure reasons why in 

 one case there is hsemorrhagic, in another white infarction, as a result of 

 em bolus. 



If the embolic material consists of or contains infectious substances, 

 such as some forms of bacteria, in addition to the mechanical effects 

 of simple emboli, we may have gangrene, suppuration, formation of 

 abscesses, etc., as the result of the local action of the infectious mate- 

 rial, even though this may be present MI very small amount. 



The organs in which embolic infarctions most frequently occur are 

 the spleen, kidney, brain, lungs; less frequently the heart, retina, liver, 

 and small intestines. Hsemorrhagic infarctions are not liable to occur in 

 the liver from emboli in the branches of the portal vein, on account of 

 the blood supply which may come to the affected region through the 

 branches of the hepatic artery. On the other hand, embolic abscesses 

 from infectious emboli are of not infrequent occurrence here. Pfcemor- 

 rhagic infarctions may occur exceptionally in regions not furnished with 

 terminal arteries, as in the small intestines. 



Cases of aberrant embolism are recorded in which venous emboli have 

 passed through an open foramen ovale into the arterial system. 



Eetrograde transportation of venous emboli has been several times 

 recorded. ' 



1 For details of unusual forms of embolism consult bibliography in Ziegler's "Gen- 

 eral Pathology," Warthin's translation of 10th Ed., 1903. 



