ABSORPTION. 219 



the lymph system, into which the vessels of the lower extremities, 

 of the abdominal organs, of the trunk, of the left arm, and of the left 

 side of the head empty their contents.} It is about twenty inches in 

 length and an eighth of an inch in diameter. ^ It exentts-"Upward 

 from the third lumbar vertebra along the vertebral column to the 

 seventh cervical vertebra, where it empties into the venous system 

 at the junction of the internal jugular and subclavian veins on the left 

 side.j^ The thoracic duct wall has the same general structure as the 

 wall of the lymph-vessel: viz., an internal or endothelial; a middle 

 elastic and muscular; an external or fibrous. It is also provided 

 with numerous valves.^ 



The lymph-vessels of the right side of the head, of the right arm, 

 and a portion of the right side of the trunk terminate in the Hgjg 

 thoracic duct, which is about 25 to 30 mm. in length and which emp- 

 ties" into the venous system at the junction of the internal jugular and 

 subclavian veins on the right side.%The general arrangement of the 

 lymphatic system is diagrammatically shown in Fig. 91. 



LYMPH. 



Properties of Lymph. The lymph obtained from the thoracic 

 duct during the intervals of digestion or from one of the large trunks 

 of the leg is a clear, colorless or slightly opalescent fluid having an 

 alkaline reaction and a specific gravity of i .020 to i .040. Examined 

 microscopically it is seen to hold in suspension a large number of 

 corrjuscles similar to those seen in the lymphatic glands and to the 

 wjute__comuscles of the blood. Their number has been estimated 

 at abouTH2oo~per cubic millimeter, though this count will vary within 

 wide limits according as the lymph examined has passed through 

 a large or small number of glands. The lymph corpuscle consists of a 

 small quantity of protoplasm in which is embedded a distinct nucleus. 

 Some of these lymphocytes contain distinct granules, more or less 

 refractive, which impart to the corpuscle a distinctly granular ap- 

 pearance. When withdrawn from the vessels lymph undergoes a 

 spontaneous coagulation, though the coagulum is, never as firm as 

 that observed in the coagulation of the blood. (The cause of the 

 coagulation is the appearance of fibrin.^ After a variable length of 

 time the coagulum separates into a liquid and a solid portion, the 

 serum and the clot. 



Chemic Composition. Although the lymph obtained from the 

 tissue spaces, from the lymph-vessels, as well as from the so-called 

 serous cavities has the same general chemic characteristics, there is rea- 

 son for the view that it varies in its ultimate composition according 

 as it is derived from one region of the body or from another. The 

 needs of any individual tissue as well as the character of its metabolic 



