THE SPLEEN AND THYMUS. 403 



cause of the redistribution of blood which is apt to occur in the viscera 

 after death. 



Hyperaemia. PASSIVE HYPER^EMIA may occur in obstruction to the 

 portal circulation, most frequently in cirrhosis of the liver, but also 

 with certain valvular lesions of the heart, emphysema, etc. The spleen 

 is enlarged, but usually only to a moderate degree. The capsule is apt 

 to be tense, and on section the pulp is dark-red and may be soft or firm. 

 The cavernous veins are dilated (Fig. 209). Usually, when the lesion 

 has existed for some time, there is a thickening of the trabeculse and 

 reticular framework of the spleen, so that these are prominent on section. 



FIG. 209. HYPERjEMIA CONGESTION OF THE SPLEEN. 



b, Dilated cavernous veins ; c, trabecula of pulp tissue compressed between dilated cavernous veins ; d, 



Klomerulus. 



In other words, there is a chronic interstitial splenitis following the 

 chronic congestion. 



ACTIVE HYPERJEMIA of the spleen, which in most cases is scarcely 

 to be differentiated from some forms of acute inflammation, and probably 

 in many cases is associated with it, very frequently occurs in a great 

 variety of acute and infectious diseases, such as typhoid fever, pneu- 

 monia, diphtheria, pyaemia, the exanthemata, etc. The spleen is en- 

 larged, the capsule tense ; on section the pulp is soft, dark-red in color, 

 often swelling out from the cut surface and concealing the glomeruli and 

 trabeculse. Under these conditions the cavernous veins are distended 

 with blood and the interstices of the pulp infiltrated with a variable, 

 sometimes large quantity of red and white blood cells. Or, in addition 

 to this, there may be hyperplasia (see below). 



Embolism and Infarction of the Spleen. Embolic infarctions of the spleen 

 are of frequent occurrence. They may be single or multiple, small or 

 very large, sometimes occupying half of the organ. They are in general 

 approximately wedge-shaped, corresponding to the area of tissue sup- 



