288 GEO. A. THIEL AND HAL DOWNEY 



ments of the blood in the splenic pulp has attracted the attention 

 of many investigators, and various methods have been devised 

 in attempting to ascertain the course of the channels that the 

 cells pursue in passing from the arterial to the venous circulation. 

 In comparing the results of previous investigations one finds 

 four different interpretations of the circulatory system through 

 the splenic pulp. 



1. An open or intermediate circulation through the pulp. 

 Upon leaving the arterial capillaries the blood passes into the 

 meshes of the network of the reticulum. These spaces connect 

 with larger ones that are differentiated into the venous sinuses 

 which in turn empty into the veins (Henle, Peremeschko, Hoyer, 

 Bannwarth, Laguesse, Kultschitzky). 



2. A completely closed circulatory system in which the blood 

 passes through the pulp in a completel}^ closed capillary system 

 (Billroth, Schweiger-Seidel, Kolliker, Kyber, Toldt, Thoma, and 

 at a later period v. Ebner, Helly, Mall (later modified)). 



3. A partially open and partially closed system (Rindfleisch, 

 Weidenreich, and Mall). Some of the blood is confined to dis- 

 tinct channels, but part of it may circulate through the reticulum 

 of the pulp before reaching the veins. 



4. A partially open system due to the porosity of the walls of 

 the venous sinuses (Mollier, J0II3", Chevalier). 



Billroth was the first to describe the splenic sinuses or venous 

 capillaries, as they were then termed. In view of the fact that 

 many splenic arteries and veins are confined. to the trabeculae, 

 Bilh'oth undertook a comparative study of a group of mammals 

 and found that in ox, sheep, and pig the trabecular material is 

 far more abundant than in rabbit, cat, and dog. In the first 

 group the veins retain a rather uniform caliber, and then suddenly 

 break up into short tapering branches that seldom anastomose 

 as they do in rabbit and cat. In the pig the lining of the veins 

 is a smooth uniform endothelium and does not bulge into the 

 lumen as in the case of the human spleen. These tiny trabecular 

 veins connect directly with the arterial capillaries, thus forming 

 a closed system. 



