LYMPH, LYMPH GLANDS, SPLEEN 89 



which enter the gland with the lymph. This prevents these 

 substances from entering the general circulation. 



The retiform tissue through which lymph passes and which 

 serves for the formation of leucocytes is also found in certain 

 other bodies, e.g. in many parts of the mucous membrane (solitary 

 glands, Peyer's patches of the intestine). 



The thymus gland has the same structure and function as the 

 lymph glands. It is well developed in the embryo and child, but 

 begins to degenerate at the tenth year and finally disappears 

 entirely. 



3. THE SPLEEN 



The spleen consists of a framework which is made of a 

 trabecular tissue and supports the spleen-pulp, a reticular 

 tissue with many cellular elements. In many places the 

 cells are clustered, forming the spleen follicles. Some of 

 the cells of the pulp are leucocytes, some are large multi- 

 nuclear cells, some are red blood corpuscles and some are 

 cells which have ingested red blood corpuscles. According 

 to most authorities, the blood is supposed to flow from the 

 capillaries into the meshes of the pulp and from there through 

 the splenic vein. 



In the capsule of the spleen there are smooth muscle fibres 

 which by their contraction regulate the size of the spleen. 



Leucocytes are formed in the spleen and thrown into the 

 blood, for the blood in the splenic vein contains more 

 leucocytes than the arterial blood. This function corre- 

 sponds to the anatomical structure of the spleen, which is. ; 

 very much similar to that of lymph glands. But white blood ^ ; 

 corpuscles are not only formed in the spleen as in the lymph 

 glands, but they are also destroyed there. This is supported 

 by the fact that we find in the spleen considerable quantities 

 of substances which have been derived from the nuclei of the 

 destroyed white blood corpuscles. They are the xanthin 

 bases, decomposition products of nuclein, which must be 

 regarded as the precursors of uric acid. If the spleen-pulp 

 is heated with blood, uric acid is formed. As it is supposed 

 that, in mammals, uric acid is formed from the nucleins of 



