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. 



lymphoid tissue. The reticular fibrillse 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 

 characteristic lymphoid cells, which 

 are the offspring of the elements 

 forming the adenoid tissue. 



The spaces of the splenicpulp 

 are sometimes occupied by num- 

 berless colored blood-cells, which 

 escape from the thin-walled vessels 

 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 

 eucocytes 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 many histologists as the birthplace, as well as the 

 "graveyard." of a certain number of colored blood-cells ; the pres- 

 ence of young nucleated red cells supports this view. 



The blp_dr.yessels 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, most of the smaller arteries leave the septa 

 and become ensheathed by the Malpighian corpuscles, to which they 

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

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

 encased within the masses of adenoid tissue. The veins lie within 

 the trabeculae which tend to subdivide the organ into units, the 

 splenic lobules of Mall, within the centre of which course the 

 terminal arterial branches. The latter enter the cords of splenic 

 cells and end in delicate and imperfectly walled channels which be- 

 come continuous with the beginning of the venous radicles within 

 the lobule. The blood-paths are directly surrounded by the lymph- 

 tissue composing the splenic cords. It is probable that under usual 

 conditions the blood is largely retained with the definite vascular 

 channels ; extravasations, however, into the spaces of the splenic 



