CHAPTER XIII 

 THE LYMPH SYSTEM. LYMPH CIRCULATION 



The lymphatic system comprises an extensive arrangement of 

 lymph vessels or lymphatics, and lymph nodes (or glands} both deep 

 and superficial (Fig. 150). 



This system pervades the entire body for the circulation of 

 lymph a nutritive fluid derived from the blood. It is by this 

 means that foods which have been absorbed from the digestive 

 organs and poured into the blood are separated out for the use of 

 the tissues and conveyed to them. 



Lymph spaces. Between the cells and collections of cells of 

 every tissue, except cuticle, hair and nails, are found minute tissue 

 spaces or lymph spaces, communicating freely with each other. 

 There are also spaces around the smallest blood-vessels and nerves 

 (called respectively perivascular and perineural spaces) . These all 

 communicate with the beginnings of lymph-capillaries (just how, 

 is disputed). 



Lymph capillaries. These resemble blood capillaries in that 

 they have but a single coat (of endothelium). They permeate the 

 tissues in every direction, forming a close network, from which 

 lymph vessels or lymphatics originate by the uniting of small 

 channels to form larger ones (as veins originate) . 



Lymph vessels. Are delicate and transparent, but have three 

 flexible coats. (One elastic, two nbro-muscular.) They are pro- 

 vided with valves, formed by folds of the lining at very short inter- 

 vals, which give the appearance of beading to the vessels. This 

 arrangement allows the lymph to flow toward the heart but pre- 

 vents it from moving in the other direction. 



The lymph vessels of the intestines have been called lacteals 

 because of their milky appearance during the process of digestion, 

 the whitish color being due to the presence of fat globules trans- 

 mitted by the lymph capillaries of the villi. This fat-bearing 

 lymph is called chyle. 



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