XI] 



ORGANS OF INTERNAL SECRETION 



149 



is partly fibrous and partly muscular, and some of the muscular 

 tissue projects into the interior of the organ in the form of 

 trabeculae. These trabeculae constitute a sort of framework in 

 which the typical spleen tissues lie. The spleen is essentially 

 a haemolymphatic gland, that is to say, a gland composed of 

 lymphoid tissue but containing also a largo number of erj'thro- 

 cytes, some of which are in a state of partial or complete dis- 

 integration. It differs from other haemolymphatic glands in 

 possessmg Malpighian corpuscles or nodules densely packed with 

 lymphocytes, each nodule surrounding an arteriole. Apart from 

 the vessels contained within the Malpighian corpuscles, all the 

 arteries communicate directly with the tissue elements of the 



Fig. 73. Section of thymus showing Hassal's corpuscles (from Schafer). 



spleen, and from this tissue the blood is gathered up anew so as 

 to flow into the splenic vein. 



The functions of the spleen are problematical. It can be 

 removed without the animal appearing to incur any harm, but 

 this may be due to other haemolymph glands (of which there 

 are often many scattered about the alimentary region) taking on 

 the splenic functions. It is knoAvn that the spleen is concerned 

 to some extent with the destruction of red corpuscles, and that 

 it contains a considerable amount of iron. It is also known that 

 in common with other lymphatic glands the spleen produces 

 leucocytes, and that uric acid is present in it in some quantitj'. 



