55^ Veteriyiary Medicine. 



splenic arteries terminate in open vascular spaces filled with 

 splenic pulp and where all trace of a freely anastomosing capillary 

 network is lost. The splenic veins in the same manner originate 

 from these open vascular spaces. There is, therefore, an absence 

 of the free communication of capillary network, which virtually 

 acts as a safet}' valve in other vascular tissues, and the vascular 

 cavities connected with each terminal artery are independent of 

 those belonging to another, and find no way of ready relief when 

 they become over distended, or when there occurs ob.struction 

 (thrombosis) of their afferent or efferent vessels. From blocking 

 of arteries or veins there is at once produced a wedge shaped area 

 of stagnation which cannot be relieved through any colateral cir- 

 culation. Again the splenic veins, being destitute of valves, 

 offer no obstacle to the reflux of blood into such vascular spaces 

 whenever the further access of blood has been arrested b}^ the 

 blocking of the artery. The blocking may occur in the afferent 

 artery through embolism by clots carried from the lungs or left 

 heart, or formed within the vessel by the colonization of microbes 

 on its walls. Even more likely is the formation of coagula in 

 the vascular spaces themselves as the result of the introduction of 

 pus, or septicasmic microbes, which are long detained and have 

 ample time for multiplication in these cavities. In either case 

 the result is obstruction to the sanguineous current, the filtering 

 of blood backward from the veins and the engorgement of the 

 cavity with blood. The plugs consist of fibrinous matter enclos- 

 ing colonies of micrococci, and the result is not only black 

 infarction of the spleen, but a subsequent general infection of the 

 system at large. 



The wedgeshaped infarcts are usually situated at the surface 

 of the organ, the base turned outward and forming a dark pro- 

 jection on the surface, and the apex turned inward. The aggre- 

 gation of two or three in one group may considerably alter the 

 outline. If recent they are of a dark red color. Later from ab- 

 sorption of the coloring matter and fatty degeneration of the 

 mass they a.ssume a pale yellow hue and the swelling flattens or 

 disappears. Later still through complete fatty degeneration they 

 may be transformed into caseated masses, or through organiza- 

 tion into fibrous tissue they may form thick white cicatrices. If 

 pus cocci are present suppuration and abscess may be the out- 

 come. 



