THE LYMPHATIC SYSTEM. 161 



THE LYMPHATIC SYS 



The Lymphatic System is a circulatory apparatus of exceedingly 

 complicated arrangement. It comprises: 



1. A system of irregular clefts and cavities which are of almost 

 universal distribution in the more solid tissues, in the framework 

 and parenchyma of organs, around tilood-vessels and viscera. 



2. Nodules of sponge-like tissue, improperly called lymphatic 

 glands. 



3. Channels of communication, consisting of capillaries and ducts. 



4. A central reservoir the receptaculum chyli. 



5. Large efferent ducts, by means of which the contents of the 

 system are, eventually, poured into the blood, in both sides of the 

 neck at the junction of the internal jugular and subclavian vein. 



6. A fluid, lymph, containing numerous nucleated bodies or 

 lymphoid cells t and various substances in solution. 



The whole provides a channel for the introduction of formed and 

 nutrient elements into the blood; as well as affording drainage for the 

 tissues, the products of which are also emptied into the blood-vascular 

 system, to be afterward eliminated by special organs. 



The circulating lymph always passes in a direction toward the ven- 

 ous system. This current is established in some of the lower animate 

 by means of distinct, pulsating, hollow organs, or lymph hearts; but 

 no corresponding structure exists in man, and the system becomes 

 here subordinated to the blood-vascular apparatus. 



In man, the maintenance of the lymph-flow is due largely to a 

 negative pressure, consequent upon the connection between the termini 

 of the lymph-vessels and the veins. Without doubt the pumping 

 motion of the intestinal villi presents a factor in the establishment of 

 a current in the lacteals toward the mesenteric vessels. The perivas- 

 cular lymph receives an impetus with each cardiac systole. The 

 muscular contractions of inspiration contribute motility to the con- 

 tents of the diaphragmatic lymph-channels, in a direction against 

 gravity. Indeed, the contractions of nearly every muscular fibre, 

 whether skeletal or organic, lend their aid to lymph propulsion. 



The direction of the lymph-current is determined by valves which 

 resemble, somewhat, those of the veins. 



Cavities lined with so-called serous membranes, may be considered 

 as expanded lymph-channels. 

 II 



