THE LYMPHATIC SYSTEM. 



125 



FIG. 152. 



Portion of channel within splenic pulp from 

 human spleen : a, endothelioid connective-tis- 

 sue plates of the imperfect wall of the space ; 

 b, red blood-corpuscles ; c, lymphoid cells ; d, 

 larger amoeboid elements, containing pigment- 

 granules ; e, large multinucleated cell. 



tissue cells. The processes of the latter unite with one another to 

 form imperfect partitions ; in young animals multinucleated plates 

 are frequently encountered. Ad- 

 hering to the delicate reticulum, 

 partially occluding the channels 

 throughout the pulp, are numerous 

 lymphoid cells or leucocytes, which 

 are largely the offspring of the ele- 

 ments forming the adenoid tissue. 



The spaces of the splenic pulp 

 are additionally occupied by num- 

 berless colored blood-cells, brought 

 by the arteries which open directly 

 into the channels within the pulp ; 

 the dark-red appearance of the 

 organ is thus explained. As a re- 

 sult of the breaking down of numer- 

 ous worn-out red blood-cells, in 

 which process of destruction the 

 leucocytes may take an active part, 

 pigment - granules, both free 

 and within the lymph-cells, are con- 

 stantly encountered. The splenic pulp, in addition to giving origin 

 to numerous leucocytes, in common with other lymphoid tissues, is 

 regarded by some histologists as the birthplace, as well as the ' ' grave- 

 yard," of a certain number of colored blood-cells; the evidence, 

 however, upon which such views rest is far from conclusive. 



The blood-vessels of the spleen form an important part of the 

 organ. After entering at the hilum, the splenic artery gives off tra- 

 becular branches which rapidly diminish in size by repeated division. 

 As already described, many of the smaller arteries leave the septa 

 and become ensheathed by the Malpighian corpuscles, to which they 

 contribute with capillary net-works. A certain number of the arteries 

 extend the entire length of the trabeculae, and hence never become 

 encased within the masses of adenoid tissue ; both these latter and 

 those bearing the corpuscles eventually open into the spaces of the 

 pulp, pouring their streams of blood into the parenchyma. The 

 pulp-spaces communicate, on the other hand, with a wide-meshed 

 net-work of venous channels ; the latter unite to form a number of 

 large veins, which pass out at the hilum in company with the principal 

 arteries. 



All the blood conveyed by the smaller arteries finally reaches the 

 spaces of the splenic pulp, whether directly or indirectly after having 

 first passed through the tissue composing the Malpighian corpuscle ; 



