THE THYMUS GLAND. 13,3 



taking quinine. Under the microscope it is seen to be composed 

 of a sponge of fibrous tissue, the spaces being filled with blood, 

 which flows freely into them from arterioles in whose walls 

 lymphoid tissue is abundant. Here and there, this lymphoid 

 tissue becomes collected in nodules, which are large enough to 

 be seen by the naked eye and are called Malpighian corpuscles. 



In the blood of the spleen, partly broken down erythrocytes 

 are often visible. Sometimes, also, cells like those found in red 

 bone marrow and having to do with the manufacture of new red 

 corpuscles make their appearance. 



Taking all these facts together, it is believed that the spleen 

 has the following functions: (1) manufacture of leucocytes; 

 (2) manufacture of erythrocytes; (3) destruction of erythro- 

 cytes; (4) removal from the blood of certain poisons. 



The Thymus Gland. The thymus gland, situated at the root 

 of the neck, is quite large at birth, but its size gradually dimin- 

 ishes as the animal -grows. By the time that puberty is reached, 

 it has almost disappeared. It is composed of peculiarly arranged 

 lymphoid tissue*, having nests of epithelial cells embedded in it. 

 It seems to bear some relationship to the generative glands, for 

 its removal in young male animals hastens the growth of the 

 testes. 



