CHAPTER XVII. 

 THE LYMPH. 



The blood circulates in closed tubules so that the nourishment 

 which is supplied the tissues and the effete products which re- 

 sult from their activity must pass through the walls of the ves- 

 sels. The fluid which is transuded from the capillaries and which 

 surrounds the cells of the tissues is known as the lymph, and 

 serves as the medium of exchange between the cells and the blood 

 plasma. It is the middleman of exchange between the blood and 

 the tissues. Lymph is a slightly yellow transparent fluid, closely 

 resembling the blood plasma from which it is derived. To aid in 

 the carrying off of any excess of lymph, there is provided a spe- 

 cial system of vessels called the lymphatics, which are very thin- 

 walled capillary tubules lined with endothelial cells. These tu- 

 bules lead to larger ones which, after passing through a lymph 

 gland along their course, finally empty into a large vein-like ves- 

 sel, the thoracic duct, lying alongside of the oasophagus in the 

 thorax, and emptying into the left subclavian vein. A smaller 

 lymphatic vessel, the right thoracic duct, empties into the right 

 subclavian vein. 



The lymph obtained from the thoracic duct by means of a fine 

 tube inserted into the vessel varies somewhat in nature. After a 

 meal the fluid is like milk, because of the presence of droplets of 

 fat which have been absorbed from the intestines. The lymphatics 

 of the viscera appear as white lines in the mesentery and on this 

 account are called lacteals. The lymph which is collected during 

 a fast is very much like the blood plasma. Its specific gravity is 

 less than that of blood, since it contains less protein material, but 

 on the other hand its salt content is the same and it clots in much 

 the same manner as blood. On microscopic examination there 

 are found many colorless corpuscles, identical to those present 

 in blood. Some of these corpuscles are formed within the lymph 



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