206 HUMAN PHYSIOLOGY 



muscle and a sponge-work of fibrous and muscular trabeculae, 

 in the interstices of which is the spleen pulp. The branches 

 of the splenic artery run in the trabeculae, and twigs, leaving 

 these trabeculse, pass out and are covered with masses of 

 lymph tissue forming the Malpighian corpuscles. Beyond 

 these, the vessels open into a series of complex sinuses from 

 which the blood is collected into channels, the venous 

 sinuses, which carry it back to branches of the splenic vein 

 in the trabeculse. The pulp is thus made up of processes 

 of fibrous tissue and of a set of branching endothelial-like 

 cells, the spaces between which are filled with blood. It is 

 comparable with the blood sinuses of the hsernolymph glands. 



So far no decrease in the number of erythrocytes in the 

 blood leaving the organ has been recorded. In the cells of 

 the spleen pulp, yellow pigment and simple iron compounds 

 are frequently seen, indicating that haemoglobin is being 

 broken down. But the idea that the spleen plays an im- 

 portant part in the actual destruction of erythrocytes seems 

 to be negatived by the fact that, when blood is injected, the 

 cells are broken down no faster in an animal with the spleen 

 than in an animal from which the spleen has been removed. 

 While the spleen appears to have no action in killing and 

 destroying erythrocytes, its cells have the power of taking 

 up dead and disintegrating erythrocytes and storing the iron 

 for future use in the body. 



The non-striped muscle in the framework of the spleen 

 undergoes rhythmic contraction and relaxation, and the 

 organ thus contracts and expands at regular intervals of 

 about a minute. 



Lymph Glands, Hsemolymph Glands, and Red Marrow of 

 Bone. When erythrocytes break down or haemoglobin is 

 injected, the pigment accumulates in these, and they there- 

 fore probably act as the graves of old erythrocytes in the 

 same way as the spleen. 



B. LYMPH. 



1. Characters of Lymph. The lymph is the fluid which 

 plays the part of middleman between the blood and the 

 tissues. It fills all the spaces in the tissues and bathes the 



