FUNCTIONAL MECHANISM OF THE SPLEEN. 387 



for, when we recall the fact that, as shown by Biedl, Dreyer, 

 and others, suprarenal activity is thereby enhanced, as shown 

 by increased secretion. The marked muscular character of the 

 spleen obviously causes it to respond by contraction to the in- 

 creased amount of oxidizing substance suddenly thrown into 

 the circulation, especially when we consider its direct connec- 

 tion with the cceliac axis. The constrictive effect of stimula- 

 tion of the medulla on the arteries we have repeatedly seen; 

 as this is due to contraction of their muscular coats, the spleen 

 is evidently influenced in a manner similar to that following 

 stimulation of the splanchnic. Again, therefore, have we as 

 underlying cause of splenic contraction suprarenal overactivity. 



But why should stimulation of the vagus also induce 

 splenic contraction? This requires an examination of the 

 distribution of the nerve-terminals. The innervation of the 

 spleen was studied by Kolliker in various animals, 13 and his 

 observations, when viewed in the light of our conceptions of 

 the functional mechanism of glandular organs, are suggestive. 

 "The vasomotor nerves enter the organ with the large arteries. 

 In the walls of the large arteries the main trunks form a well- 

 marked superficial plexus with oblong meshes in the adventitia, 

 and a deep, more quadrate net-work in the tunica media; some 

 end in the little branched arborizations in this coat. The 

 smaller arteries and the trabeculae receive their nerves from 

 the rich maze of fibers in the pulp, consisting of axis-cylinders, 

 which, however, do not anastomose. Other fibers form a 

 plexus on the surface of the trabeeulaB, and from this fibrils 

 penetrate into the interior of the trabeculae (which contain 

 much smooth muscle) and end by free arborizations." Free 

 terminals, which Kolliker regards as sensory fibers, were also 

 found. When we consider that the trabeculse penetrate deeply 

 into the interior of the organ from the inner surface of the 

 capsule in every direction, thus forming a spongy frame-work, 

 it seems clear that stimulation of the nerves distributed to 

 these structures and to the vascular walls should produce gen- 

 eral contraction. 



These data would not be sufficient to enable us to assimi- 



18 Kolliker: Sitzungsbericht d. Wttrsb. Phys. med. Gesellschaft, No. 2, 1893. 



