THE CIRCULATORY SYSTEM. 449 



penetrating wound may be fatal if the vessel be large. The wound of a 

 small artery may close or a false aneurism may develop at its seat. 



In the healing of a wounded artery the vessel retracts and contracts, 

 and a thrombus is formed within it. The contraction alone may be suffi- 

 cient to close the vessel ; its coats thicken, and the. inner surfaces finally 

 are fused together ; or the blood coagulates and forms a thrombus in the 

 vessel near the wound. This thrombus later becomes organized and the 

 vessel is converted into a fibrous cord. 



DEGENERATION. 



Fatty Degeneration. This may occur in the walls of otherwise unal- 

 tered vessels, or in those which have undergone a variety of inflamma- 

 tory or degenerative changes. It may occur either in the intima or 

 media, or both, and may be so extensive as to form a very prominent 

 gross lesion, or so little developed as to require the microscope for its 

 recognition. When marked, especially if occurring in the intima of 

 large vessels, smaller and larger spots or stripes or patches may be seen, 

 of a yellowish-white color, usually sharply circumscribed, and sometimes 

 smooth, sometimes roughened on the surface. It is most apt to occur in 

 the aorta, but may be found in any of the vessels. In moderate degrees 

 of the lesion we find on section that the cells of the intima contain fat 

 droplets in greater or less number. When further advanced, not only 

 are the cells crowded with fat droplets, but the intercellular tissue also 

 may be more or less densely infiltrated with them. Sometimes the infil- 

 tration is so dense that the tissue breaks down, and there may be an ero- 

 sion of the surface, forming a so-called fatty ulcer. When the media is 

 involved the muscle cells contain fat droplets. It may lead to the for- 

 mation of aneurism or .to rupture of the vessels. 



Amyloid Degeneration, which may affect all the coats of the arteries, 

 but especially the intima and media, has already been described in gen- 

 eral (page 82). It will be further considered under the lesions of the 

 organs in which it most commonly occurs. 



Hyaline Degeneration may cause thickening of the intima of the blood- 

 vessels by its conversion into or infiltration with a homogeneous material 

 somewhat similar to amyloid (see page 86). Or it may involve the entire 

 wall of smaller vessels, converting them into irregular lumpy cords. 

 The lumen of vessels thus changed may be obliterated or occluded by 

 thrombi. 



Calcification usually occurs in vessels otherwise diseased, and may 



involve either the intima or media. It consists in the deposition of salts 



of lime either in rhe cells or intercellular substance. The lime may be 



in the form of larger or smaller granules or in dense translucent plates. 



29 



