300 THE HUMAN BODY 



nective tissue, part fibrous and part elastic, interspersed with 

 smooth muscle-fibers. Projections of the sheath extend into the 

 cavity of the organ, subdividing it into numerous spaces; these 

 are filled with masses of cells which make up the spleen pulp. 

 Numerous blood-corpuscles, both red and white, are found mingled 

 with the cells of the spleen pulp. The spleen has a very rich blood 

 supply which differs from that of all other organs of the Body in 

 that the small arteries instead of communicating with capillaries, 

 which lead in turn into veins, open directly into the spleen pulp. 

 This tissue is bathed, therefore, with blood instead of with lymph 

 as are all other tissues. The spleen pulp is drained by tiny veins 

 which collect the blood into larger ones and so return it to the 

 portal vein (p. 335) whence it passes through the liver and so on 

 into the general circulation. 



Function of the Spleen. The peculiarly intimate way in which 

 the spleen cells are brought into relationship with the blood suggests 

 that the organ is specially concerned somehow in maintaining the 

 normal constitution of the blood. Moreover, this concern would 

 appear to be with the formed elements rather than with the plasma, 

 for the delicate membranes which form the capillary walls, and 

 which, in all organs except this, stand between the blood and the 

 tissue cells, oppose no difficulty to the passage of dissolved sub- 

 stances, but only to the passage of corpuscles. The spleen is the 

 only region, then, aside from the red marrow, in which they were 

 formed, that the red corpuscles have direct contact with tissue 

 cells, other than those that form the lining membrane of the blood- 

 vessels. The most satisfactory theory of spleen function that we 

 have is that it picks out from the blood stream and disintegrates 

 those red corpuscles that are "worn out" and no longer able to 

 carry on efficiently their function as oxygen carriers. In support 

 of this theory is the observation that the spleen always shows 

 within its meshes numerous cells that have engulfed red corpuscles 

 and are apparently in the process of disintegrating them. More- 

 over, in some cases of pernicious anemia, a blood disease in which 

 there is excessive destruction of red corpuscles, virtual cures have 

 been wrought by operative removal of the spleen. The hemoglobin 

 that is set free by the disintegration of the corpuscles is carried to 

 the liver and there decomposed as described above. 



The spleen shows rhythmic contractions and relaxations which 



