MICROSCOPIC ANATOMY OF THE ORGANS. 



diate space is, according to some authors, lined with epithelium, 

 so that there is here a closed system. Most authorities, how- 

 ever, claim that these lacuna have no wall or possess only an 

 incomplete wall, so that the blood does not flow in a closed 

 channel. These authors base their belief on the fact that in 

 injecting the blood-vessels the injection mass flows also into the 

 spleen pulp; and because of the constant presence of red blood- 

 corpuscles in the pulp. According to the view held by the 

 second group of investigators, the beginnings of the veins stand 

 in communication with spleen pulp. These endothelial cells 

 are flattened and spindle-shaped, and show a striated structure. 

 The nuclei project markedly into the lumen. According to 

 Weidenreich, there is a system of spaces (spleen sinuses) in the 

 spleen pulp which anastomose freely and open into the pulp 

 veins (intralobular). 



The framework of the spleen pulp is made up of anasto- 

 mosing fibrils which have the character of reticulum, as shown 

 by Mall. As mentioned before, the reticulum of the capsule 

 and trabeculae is more resistant to the action of the ordinary 

 reagents than that of the spleen pulp. " The main strands of 

 the reticulum accompany the interlobular venous plexus, while 

 a more delicate network with more open meshes extends 

 through the histological unit. In the centre of the unit the 

 network becomes dense again, which marks the position of the 

 terminal artery with its accompanying ellipsoid lymphatic 

 tissue" (Mall). The reticulum surrounds the veins, and also 

 forms a layer around the arteries, holding in its meshes the 

 cells of the lymphoid sheath. Kyes has shown that the net- 

 work surrounding the smaller veins is not. elastic tissue, but is 

 made up entirely of true reticulum. The reticulum of the 

 follicles is directly continuous with that of the pulp cords. 



Lymphatic vessels in relation to the Malpighian follicles do 

 not exist in the spleen. In the capsule and trabeculee of the 

 spleens of certain animals there are large lymphatic channels. 

 These are seen also at the hilus of the organ, but, according 

 to Mall, the lymphatics are not to be observed in the spleen 

 pulp. 



