188 



THE ORGANS 



B 



these arteries are known as central arteries. They give rise to a few 

 capillaries in the spindles, to a larger number in the nodules. Be- 

 yond the latter the arteries divide into thick sheathed terminal 

 artenes— -pulp arteries — wliich do not anastomose, but lie close to- 

 gether like the bristles of a brush or penicillus. The pulp arteries 

 break up into unusually thick walled arterial capillaries which still 

 retain an adventitia, the so-called sheathed arteries. These are of re- 

 markably uniform diameter — 6-8 cc — and empty into broader spaces 

 from lo to 40yu in diameter — the spleen sinuses or ampiillcB — which in 

 turn empty in to the cavernous veins of the splenic pulp (Fig. no). 

 The Splenic Pulp. — The anastomosing cavernous veins break 

 up the diffuse lymphatic tissue of the spleen into a series of anasto- 

 mosing cords similar to those found in the medulla of the lymph 

 node. These are known as pulp cords (Fig. no), and with the caver- 

 nous veins constitute, as already mentioned, the splenic pulp. The 

 pulp cords consist of a delicate framework of reticular connective 



tissue, in the meshes of which are 

 found, in addition to lymphoid 

 cells, the following (Fig. 112): 



(i) Red blood cells, including 

 nucleated red blood cells and 

 fragments of red cells in process 

 of disintegration. 



(2) White blood cells. 



(3) Mononuclear cells, the 

 so-called spleen cells. These 

 are rather large, granular, spher- 

 ical, or irregular cells. From 

 the fact that blood pigment and 

 red blood cells in various stages 

 of disintegration are found in 

 their cytoplasm, these cells are 

 beheved to be concerned in the 



destruction of red blood cells. 



(4) MuUinuclear cells. These are most common in young ani- 

 mals. Each cell contains a single large lobulated nucleus, or more 

 frequently several nuclei. These cells resemble the osteoclasts of 

 developing bone and the multinuclear cells of bone-marrow. 



In macerated splenic tissue or in smears from the spleen, there 

 are found, in addition to the above varieties of cells, long spindle- 



J? 





H 



a 



\ 



F 



(■;■. 





di 



Fig. 112. — Isolated Spleen Cells. X700. 

 (KoUiker.) A, Cell containing red blood 

 cells; b, blood cell; k, nucleus; B, leucocyte 

 with polymorphous nucleus; C, "spleen" 

 cell with pigment granules; D, lymphocyte; 

 E, large cell with lobulated nucleus (megalo- 

 cyte); F, nucleated red blood cells; G, red 

 blood cell; //, multinuclear leucocyte; /, cell 

 containing eosinophile granules. 



