346 THE HUMAN BODY 



of the jugular and subclavian veins. The trunk on the right side is 

 much smaller than the other and is known as the " right lymphatic 

 duct." It collects lymph from the right side of the thorax, from 

 the right side of the head and neck, and the right arm. The lymph 

 from all the rest of the Body is collected into the thoracic duct. It 

 commences at the upper part of the abdominal cavity in a dilated 

 reservoir (the receptaculum chyli) , into which the lacteals from the 

 intestines, and the lymphatics of the rest of the lower part of the 

 Body, open. From thence the thoracic duct, receiving tributaries 

 on its course, runs up the thorax alongside of the aorta and, passing 

 on into the neck, ends on the left side at the point already indi- 

 cated; receiving on its way the main stems from the left arm and 

 the left side of the head and neck. The thoracic duct, thus, brings 

 back to the blood much more lymph than the right lymphatic duct. 



Lymph-Nodes. At intervals along the course of various 

 lymphatic vessels are structures consisting of cells so arranged 

 as to leave interspaces among them, through which interspaces 

 the lymph is forced to flow. These structures are the lymph-nodes 

 or lymph-glands and the peculiar tissue of which they are com- 

 posed is lymphoid or adenoid tissue. Lymph-nodes occur in the 

 neck, the groin, the axilla and in various other regions of the 

 Body. Certain structures in the wall of the small intestine near 

 its lower end, the so-called Peyer's Patches, are composed of 

 lymphoid tissue as are also the structures in the throat making 

 up the tonsillar ring. 



Functions of Lymph-Nodes. Two quite different functions 

 are attributed to the lymph-nodes. They are supposed in the 

 first place to be the seat of leucocyte production. When any 

 lymph-node is examined its spaces are usually found filled with 

 leucocytes, some of which are in process of division. This process 

 has been observed in leucocytes in lymph-nodes but not else- 

 where, and since it is agreed that leucocytes are produced by the 

 division of parent ones, the lymph-nodes are looked upon as the 

 regions where this goes on. 



The lymph-nodes have also the additional function of filtering 

 the lymph that passes through them. This filtering action is 

 probably of great importance in confining micro-organisms to the 

 region which they first- enter, since if they get into the lymph 

 stream they are arrested at the first lymph-node. It is thought 



