1246 PHYSIOLOGY 



cells, and leucocytes. Just as in a lymphatic gland the cellular elements of 

 the tissues are bathed by the lymph which flows through the gland, so in the 

 spleen the walls of the capillaries become discontinuous, and the blood is 

 poured out into the interstices of the tissue. The spleen is therefore the 

 only tissue in the body where the blood comes in actual contact with the 

 tissue elements themselves. The blood from the splenic pulp is collected 

 into large venous sinuses, which run along the trabeculse to the hilum, where 

 they unite to form the splenic vein. The arteries to the spleen are beset in 

 their course along the trabeculae with small nodules of lymphoid tissue, which 

 are known as the Malpighian follicles. 



It is evident that the blood must meet with considerable resistance in 

 passing through the close mesh work of the splenic pulp. In order to ensure 

 a constant circulation through the gland, the muscular tissue of the capsule 



FIG. 564. Plethysmographic tracing of spleen (upper curve) from a dog, showing the 

 spontaneous contractions of this organ. (Reduced from a tracing by SCHAFER.) 



and trabeculae has the property of rhythmic contraction. If the spleen be 

 enclosed in a plethysmograph or splenic oncometer, and its volume be 

 recorded by connecting this with an oncograph, it will be seen to be subject 

 to a series of large slow variations, each contraction and expansion lasting 

 about a minute and recurring with great regularity (Fig. 564). Superposed 

 on these large waves are smaller undulations due to the respiratory variations 

 of the blood pressure, and on these again the little excursions corresponding 

 to each heart beat. The contractile power of the spleen is under the 

 control of the nervous system, and a rapid contraction may be induced by 

 stimulation of the splanchnic nerves. 



FUNCTIONS OF THE SPLEEN 



The structure of this organ suggests that the splenic cells must exercise 

 a constant influence on the blood which surrounds them, and that this 

 influence is not purely of a chemical nature. In the liver and kidneys, 

 which exercise so powerful an effect on the composition of the blood passing 

 through them, the proper cells of the organs are separated from the blood 

 stream by the capillary wall. Microscopic examination of the cells of the 

 splenic pulp shows us that these are full of particles of brown pigment 

 or fragments of red corpuscles (Fig. 565). In many cases of infectious 



