406 THE SPLEEN AND THYMUS. 



plied by the occluded artery (Fig. 14, p. 76). They may be hsemor- 

 rhagic, i.e., red, or they may be white. Infarctions, originally red, may 

 become white after a time from changes in the blood pigment. They may 

 usually be seen as dark-red, reddish-white, or white, hard, sometimes 

 slightly projecting areas on the surface of the organ. Not infrequently 

 the centre of the infarction is light in color, w r hile the peripheral zone is 

 dark-red. A layer of fresh fibrin is sometimes seen over the surface of 

 the infarction. The general as well as the microscopical appearances 

 which they present depend largely upon the age of the infarctions. In 

 the earlier stages the hsemorrhagic infarctions present little more under 

 the microscope than a compact mass of red blood cells, among which 

 may be seen the compressed parenchyma. The w T hite infarction may 

 show at first an outline of the splenic structure, but the entire tissue is 

 in a condition of coagulation necrosis. The tissue may disintegrate and 

 soften, and be more or less completely absorbed, with or without fatty 

 degeneration. A zone of inflammatory tissue may appear around the 

 infarction and upon the capsule, and this tissue, becoming denser, as- 

 sumes the characters of a cicatrix and contracts around the uuabsorbed 

 remnant of the infarction, so that finally nothing may be left but a dense 

 mass of fibrous tissue, which frequently draws in the surface, causing 

 more or less distortion of the organ. This cicatrix may be pigrnented or 

 white. 



If the embolus be infective, in addition to its mechanical effects there 

 may be suppuration, gangrene, and the formation of abscess. There 

 may be perforation of the capsule and fatal peritonitis. Infarctions of 

 the spleen may follow thrombosis of the splenic vein. 



Thrombosis of the splenic vein is rare as a primary lesion, but it 

 may be of secondary occurrence in connection with portal or mesenteric 

 thrombosis, with other lesions of the spleen, or with acute inflammation 

 of the pancreas. Thrombosis of the splenic vein has been reported fol- 

 lowing typhoid fever. 



INFLAMMATION. 



Inflammatory Hyperplasia (Acute Hyperplastic Splenitis, Acute Splenic 

 Tumor). The conditions under which hyperplasia and acute inflamma- 

 tion of the spleen occur have already been mentioned under active 

 hypersemia, with which it is usually associated. It is a frequent though 

 not a constant accompaniment of the acute infectious diseases. The 

 spleen is enlarged, sometimes to two or three times its normal size. On 

 section the pulp is soft, often almost diffluent, and projects upon the cut 

 surface. The color is sometimes dark-red, sometimes grayish-red, or 

 mottled red and gray. The trabeculse and glomeruli are usually concealed 

 by the swollen and softened pulp, but the glomeruli are sometimes 

 unusually prominent. 



Microscopical examination shows the marked increase in size to be 

 due in part to the hyperaemia ; in part to a swelling and increase in the 

 number of cells, sometimes of the pulp, sometimes of the glomeruli, or 



