SECRETION. 



417 



trabeciilae pass inward toward the center of the organ. In their 

 course they give off a series of processes which unite freely, forming 

 a spongy connective-tissue framework. The capsule and the main 

 trabeculae in some animals contain numerous non-striated muscle- 

 fibers. In man they are relatively few in number. The blood- 

 vessels which enter the spleen are supported by the connective- 

 tissue septa. As they pass toward the center of the organ they 

 divide very rapidly and soon diminish in size. In their course small 

 branches are given off, which penetrate the intertrabecular tissue, 

 and become encased with spheric or cylindric masses of adenoid 

 tissue known as Malpighian corpuscles. These corpuscles are 

 composed largely of leukocytes. In some animals the leukocytes, 

 instead of being arranged 

 in masses, are distributed 

 along the walls of the 

 artery as a continuous layer. 

 Within the corpuscles the 

 arteries pass into capil- 

 laries, whether the artery 

 passes directly to the splenic 

 pulp or indirectly by way of 

 the corpuscles, its ultimate 

 branches terminate in capil- 

 laries which open into the 

 spaces of the splenic pulp. 

 From these spaces a net- 

 work of venules gathers the 

 blood and transmits it to 

 the veins. It is a disputed 

 question as to whether the 

 spaces are lined by epithe- 

 lium, thus forming a con- 

 tinuous blood channel, or whether they are wanting in this histologic 

 element. 



The Splenic Pulp. The spaces of the connective- tissue frame- 

 work are filled with a dark red semifluid mass known as the splenic 

 pulp. When microscopically examined, the pulp presents a fine 

 loose network of adenoid tissue, large numbers of leukocytes or 

 lymph corpuscles, red corpuscles in various stages of disintegra- 

 tion, and pigment granules. Chemic analysis reveals the presence 

 of a number of nitrogen-holding bodies, e. g., leucin, tyrosin, xanthin, 

 uric acid; organic acids, e. #., acetic, lactic, succinic acids; pigments 

 containing iron, and inorganic salts. 



The Functions of the Spleen. Notwithstanding all the ex- 

 periments which have been made to determine the functions of the 

 27 



FIG. 190. MALPIGHIAN CORPUSCLE OF A CAT'S 

 SPLEEN INJECTED, a. Artery, b. Meshes 

 of the pulp injected, c. The artery of the 

 corpuscle ramifying in the lymphatic tis- 

 sue composing it. 



