248 



THE LYMPHATIC SYSTEM 



denser cords of uncertain outline, the splenic pulp cords, and slightly 

 looser intercordal pulp, the venous sinuses, corresponding to the sinuses 

 of the medulla of lymph nodes. The penicilli are located in the pulp 

 cords. Terminally these penicilli expand into dilatations, the ampullce 

 of Thoma. 



The exact method of passage of the blood from the terminal arterioles 

 to the initial venules is uncertain and disputed. It is certain only that 

 blood passes freely at this point into the splenic pulp. This gives the 

 adenoid tissue a deeply red or purple color, in contrast to the light pink 

 color of ordinary lymph nodes, due to the presence of innumerable ery- 



throplastids. It seems prob- 

 fi able that the walls of the con- 



> necting capillaries and the ini- 



tial venules (cavernous veins, 

 venous sinuses) are fenestra- 

 ted, permitting the free pas- 

 sage of blood from these vessels 

 into the spleen pulp. 



According to some au- 

 thorities the blood passes 

 by two routes from the 

 arterioles to the venules; 

 (1) through the arterial 

 ampullae directly into the 

 venules (venous ampullae) ; 

 and (2) from other ter- 

 minal arterial twigs into 

 the spleen pulp, from where it is collected by the venules. 



The veins thus begin as wide sinusoidal channels (pulp veins) within 

 the splenic pulp. At first, and for a considerable distance, they follow 

 an independent course through the pulp, receiving at the same time 

 frequent accessions of blood from other venous radicals. Finally, how- 

 ever, the veins enter the larger trabeculse, but are still devoid of more 

 complete coats than the thin membrane of fibro-elastic tissue which sur- 

 rounds the endothelial tube, but which is now ensheathed by the trabecu- 

 lar tissue. Henceforth the path of the veins lies within the trabeculaa 

 (interlobular veins), and is directed toward the hilum. On approaching 

 the hilum the larger veins acquire the usual venous coats. Having ar- 

 rived at the hilum, they form several efferent vessels which, in the out- 

 lying connective tissue, form by their union the splenic vein. 



FIG. 252. THE ORIGIN OF A VEIN IN THE 

 SPLENIC PULP. 



a, venous endothelium ; b, leukocytes; c, 

 red blood corpuscles (appearing rather too 

 dark in the reproduction); d, a mesh of the 

 splenic pulp. Highly magnified. (After 

 Bannwarth.) 



