THE SPLEEN. 



lymphoid tissue, the splenic nodules or Malpighian bodies. Depending upon 

 the plane of section, these nodules appear in preparations of the spleen as 

 irregular round or elongated deeply staining tracts, in which the artery 

 usually lies somewhat eccentrically. During its course through the nodule, 

 the artery gives off lateral branches which are resolved into capillaries that 

 pierce as well as supply the ensheathing lymphoid tissue. 



The terminal twigs of the artery are the small short vessels, known as 

 the pulp-arterioles, which enter the anastomosing strands of lymphoid tissue, 

 the pulp-cords, that, together with the blood-spaces, constitute the splenic 

 pulp occupying the intervals of the fibrous framework. After repeated 

 branching, the pulp-arterioles give rise to arterial capillaries possessed of 

 relatively thick walls. The further course of the blood-stream probably 

 varies, since some of the arterial capillaries become directly continuous with 

 enlarged thin-walled channels, the ampulla or splenic sinuses, which lie 



Germ-centre 



Pul 

 cord 



Venous space 



FIG. 155. Section of splenic nodule, showing its relations to surrounding pulp-tissue. X 120. 



between the pulp-cords and convey the blood into the wide venous capillaries 

 that constitute the commencement of the more definite intralobular veins. 

 Other of the arterial capillaries and the capillaries coming from the splenic 

 nodules lose their walls, the blood escaping into the splenic pulp, which 

 thus becomes infiltrated with great numbers of erythrocytes and consequently 

 appears of a deep red tint. After slowly welling through the pulp, during 

 which passage the effete erythrocytes are attacked and destroyed by the 

 phagocytic lymphoid cells, the blood passes by narrow channels into the 

 venous spaces and radicles forming the intralobular veins. It is probable, 

 therefore, that while one part of the Hlood brought to the spleen finds its 

 way actually into the splenic pulp, another part may pass, byji closed path\v 

 and under usual conditions, from the arteries into the veins, without ming- 

 ling with the lymphoid elements of the splenic pulp. The intralobular veins 

 are tributary to the larger interlobiilar veins, which occupy the interlobular 

 trabeculse and, finally, emerge at the hilum as the branches of the splenic vein. 

 The splenic pulp consists of an intricate complex made up of a deli- 

 cate supporting reticulum, continuous with the terminal ramifications of the 

 intralobular trabeculae, and the cells contained within and supported by the 

 meshwork, together with the thin-walled splenic sinuses and venous chan- 

 nels. The pulp-cells include a variety of elements, the most constant of 

 which are: (a) lymphocytes; (6) leucocytes of the mononuclear and poly- 



