DEVELOPMENT OF THE MAMMALIAN SPLEEN 289 



Among the more recent workers, we find Helly still an ardent 

 supporter of the closed circulatory system. Helly admits the 

 presence of blood-cells in the splenic pulp, but maintains that the 

 walls of the vessels are very permeable and that the endothelial 

 cells rest upon a structureless membrane through which the blood- 

 cells can readily pass. The presence of such a membrane is 

 denied by Billroth, Schweigger-Seidel, and Maugubi-Kudrjavt- 

 zewa, but its presence is maintained by v. Ebner, Schumacher, 

 and Weidenreich. 



Mall studied the spleen of cat and dog and found the following : 

 ''from numerous specimens its (the artery's) communication with 

 the vein is not large but is cut up by bridges of tissue across its 

 lumen before it connects with the vein. This cutting up is so 

 extensive that in uninjected specimens it has been impossible 

 for me to find a single ampulla cozmected with a vein. In other 

 words it may be better to say that the ampulla rarely reaches the 

 vein but is separated from it by a small band of splenic pulp." 



Weidenreich concludes that two distinct routes are open be- 

 tween the arterial and venous portion of the splenic circulatory 

 system. A branch of the splenic artery, upon leaving a trabec- 

 ula, forms branches that do not anastomose. These branches 

 soon acquire a lymphoid sheath which at certain intervals forms 

 splenic follicles. Beyond the follicle the artery is resolved into 

 numerous 'Pilsenarterien' each of which shows a distinct capsule 

 near its extremity. It is beyond the capsule that the true arterial 

 capillaries are found. The capillary may empty directly into a 

 splenic sinus, or its contents may be poured into the meshes or 

 spaces of the reticulum of the pulp and collect in larger channels 

 which lead into the venous sinuses of the organ. 



Mollier gives a detailed account of the capillary veins in the 

 spleen of dog, cat, ox, ape, and man. In the spleen of dog, cat, 

 and pig, the sinuses possess no distinct endothelium, but are 

 merely lined with cells of the reticulum of the pulp. These 

 cells retain then original reticular structure and consequently 

 many of the spaces between neighboring cells serve as channels 

 leading from the pulp into the sinuses. 



