n6 



NORMAL HISTOLOGY. 



morphonuclear types; (r) red blood-cells; (cT) phagocytic cells containing 

 disintegrating red-cells or pigment particles derived from the destruction of 

 the same; and (e) few large megakaryocytes. A variable amount of free 

 pigment from the disintegrated red cells is also present. During embryonic 

 life, and perhaps later in response to unusual demands for new red blood- 

 cells (as after severe hemorrhage), the spleen is the birth-place of new 

 red cells; these are at first nucleated, but soon lose their nuclei. The ele- 

 ments forming the imperfect endothelial lining of the ampullae or splenic si- 

 nuses are peculiar in being elongated and possessed of nuclei which project 

 into the lumina of the channels. They are sometimes called splenic fibres 

 and are said to be contractile. The reticular tissue is disposed around the 

 splenic sinuses and venous . radicles in rings which probably support and 

 prevent collapse of the delicate channels. The splenic nodules correspond 

 in structure with the cortical nodules of lymph-nodes and often enclose 



Arteriole 



Pulp-cords 



Venous space 



Reticulum 



Arteriole 



FIG. 156. Section of spleen, showing details of pulp-tissue. X 300. 



germ-centres. Since within the spleen many worn-out erythrocytes are 

 destroyed and new lymphocytes are produced, it is evident that the blood 

 carried away from the organ by the splenic vein is poorer in red and richer 

 in white cells than that brought by the splenic artery. 



The lymphatics are represented by a meagre set of superficial vessels, 

 which lie beneath the serous membrane and converge towards the hilum. 



The nerves, derived from the sympathetic solar plexus, include many 

 nonmedullated fibres. For the most part they are sympathetic fibres des- 

 tined for the unstriped muscle within the walls of the blood-vessels and 

 within the trabeculse. They enter at the hilum and accompany the branches 

 of the splenic artery. Delicate nonmedullated fibres have been described 

 within the splenic pulp, some of which are presumably sensory in function. 



Accessory spleens are common, but they are not all of the same 

 significance. Some are isolated parts of the spleen, which have become 



