106 STUDENTS HISTOLOGY 



THE LYMPHATIC SYSTEM 



The Lymphatic System is a circulatory apparatus of exceed- 

 ingly 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, and around blood-vessels and viscera. 

 They are called lymph -spaces or juice -canals. 



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

 glands. 



3. Channels of communication, consisting of capillaries and 

 larger vessels called lymphatics. 



4. A central reservoir the receptaculum chyli. 



5. Large efferent lymphatics, 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 sub- 

 clavian veins. 



6. A fluid, lymph, containing numerous lymphoid cells, and 

 various substances in solution. 



The whole provides a channel for introducing formed and nu- 

 trient elements into the blood, and for conveying nutrition to the 

 cells, 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 

 venous system. This current is established in some of the lower 

 animals by means of distinct, pulsating, hollow organs, or lymph- 

 hearts; but no corresponding structure exists in man, and the sys- 

 tem 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 perivascular lymph receives an impetus with each 

 cardiac systole. The muscular contractions of inspiration con- 

 tribute motility to the contents of the diaphragmatic lymph -chan- 

 nels, in a direction against gravity. Indeed, the contractions of 

 nearly every muscular fiber, whether skeletal or organic, lend their 

 aid to lymph- propulsion. 



