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HANDBOOK OF PHYSIOLOGY -^ CIRCULATION II 



fig. 15. An ampulla of a red pulp artery. 

 [From Peck & Hoerr (94).] 





fig. 16. Diagram summarizing the main types of arterio " 

 venous connections in the mouse spleen. [From Peck & Hoerr 



(94)-] 



but proper focusing shows them to be within tortuous 

 capillaries. 



Peck and Hoerr conclude from their observations 

 that blood in the spleen passes through lined, intact 

 blood vessels which join the arterial and venous 

 systems. 



The next major reports on intermediate circulation 

 in the spleen were by Parpart et. al. (93) and Whipple 

 et al. (133), and favored open circulation. These 

 investigators saw three ways in which trabecular 

 arteries, terminating as arterioles, connected with 



collecting veins. Most of the arterioles spewed blood 

 through funnel-shaped openings into large pulp 

 spaces from which the blood flowed into collecting 

 veins. Some of the arterioles made direct connection 

 with collecting veins, and such connections were 

 called arteriolar-venous anastomoses. A few of the 

 arterioles were seen to branch into a loose, irregular 

 capillary network which formed venules that returned 

 to the collecting veins. Considering each component 

 of the system from arteriole to veins separately, 

 Parpart et al. (93) state the following: Terminal 

 arterioles are thick and muscular and show con- 

 tinuous diameter changes clue to constriction and 

 relaxation of the vascular muscle. The terminations 

 of these arterioles are usually three-dimensional and 

 funnel-shaped with the flared ends becoming too thin 

 to be seen with the microscope. This indicates, 

 according to Parpart et al., that the flare thins out to 

 a condition of no endothelial covering of the blood 

 that flows out of the ampulla into the pulp. The pulp 

 space may be fed by only one arteriole or by several. 

 Pulp (reticular) cells are scattered throughout the 

 space seemingly held in position by connective tissue 

 strands. Red and white blood cells can be seen to 

 enter and leave the main stream of blood flowing 

 through the pulp space, remaining outside the stream 

 and thus stationarv for variable periods. The pulp 

 spaces are interconnected as shown by the passage of 

 blood cells between them. Collecting veins are seen 

 in the pulp spaces at positions opposite to the arteriole 

 entrance, receiving blood through end and lateral 

 openings in their walls. The lateral openings are 

 large enough in some instances to allow the passage 



