162 THE LYMPHATIC SYSTEM 



3. Polynuclear neutrophile leucocytes, similar to those of the 

 blood. 



4. EosinopTiile leucocytes, with numerous coarse acidophile 

 granules and a polylobular nucleus. This variety is more fre- 

 quent than in any other lymph oid tissue except the bone marrow. 



5. Basophile leucocytes, mononuclear or polynuclear, but with 

 a considerable basophilic rim of cytoplasm. 



6. Phagocytes, either mononuclear or polynuclear, with a broad 

 ring of cytoplasm, within which are found coarse pigment granules, 

 fragments of disintegrated red blood cells and even entire blood 

 corpuscles, fat droplets, and in diseased conditions bacteria. 



7. Giant cells, megakaryocytes, with a polylobular nucleus and 

 a very broad rim of cytoplasm. Bed blood corpuscles and fat 

 droplets have also been found in these cells. 



8. Red Uood corpuscles, erythrocytes, occur in great abundance ; 

 they are derived from the blood. They are found not only within 

 the thin-walled vessels of the pulp but also in the spaces of the 

 reticulum, where, if the slightest congestion of the organ is pres- 

 ent, they are so numerous as to outnumber the other cell types. 



9. Nucleated red Uood corpuscles, erythrollasts. The embry- 

 onic spleen contains true " blood islands " in which erythroblasts 

 are actively formed. In the normal spleen of adult man, as well 

 as of other mammals, nucleated red blood cells appear to be quite 

 constantly present, though in relatively small numbers. 



10. Blood platelets, thrombocytes and thromboblasts, are of fre- 

 quent occurrence. They are probably derived from the blood. 



Blood supply. The further structure of the spleen is closely 

 connected with its blood supply. 



The arteries enter the hilum of the organ in a group, and fol- 

 lowing the branching trabeculae reach all portions of the organ. 

 The arterial bifurcations are not always coincident with the sub- 

 division of a trabecula, so that the latter, instead of including a 

 blood vessel, form solid columns of fibro-muscular tissue. 



The wall of the trabecular arteries of the spleen is rich in 

 smooth muscle, the fibres of which are circularly disposed. The 

 adventitia is loose, thin, and firmly adherent to the substance of 

 the trabecula in which the vessel lies : it contains a system of 

 perivascular lymphatics and tissue spaces. 



The smaller branches of these arteries finally leave the trabec- 

 ulae to pass directly into the spleen pulp. Within this tissue their 

 muscular coat becomes much thinner, and their adventitia is re- 



