Chap. 12 CIRCULATION AND TRANSPORTATION BODY FLUIDS 213 



cacy. When the pressure becomes high in lymph capillaries and tissue spaces, 

 the fluid filters into the blood capillaries and joins the plasma. 



Lymph flows in only one general direction, toward the heart. In its course 

 it runs through larger and larger vessels finally converging in the left thoracic 

 duct that empties into a large vein in the left shoulder — in man, at the junction 

 of the left jugular and subclavian veins (Fig. 12.12). Thus, lymph continually 

 filters out of the blood and then returns to it by a large inflow, as well as by a 

 refiltering through capillary walls. Blood flows away from the heart through 

 arteries and capillaries, but its fluid content returns not only as blood through 

 capillaries and veins, but as lymph through the lymph vessels. 



Lymph vessels are provided with efficient bacteria traps in the many lymph 

 nodes that are located along the vessels (Figs. 12.13, 12.14). Each of them is 

 a labyrinth of lymphatic tissue in which lymphocytes are produced. In its regu- 

 lar course lymph flows slowly through these mazes populated with phagocytes 

 which attack and engulf such bacteria and foreign particles as may be passing 

 by. Dense lymphatic tissue is abundant about the throat (e.g., the tonsils) and 

 respiratory passages, and in the intestinal wall, places where bacteria abound. 

 In an infected thumb the lymph vessels become inflamed and hinder the 

 circulation of the blood so that red streaks extend up the inner side of the 

 arm to the elbow where there are good chances that the poisons may be 

 caught in the lymphatic tissue, kept out of the general circulation, and ulti- 

 mately destroyed. 



Lymph moves slowly through the vessels pushed along by the volume 



Fig. 12.12. The relationship between the blood and lymph circulations (the 

 latter in black). Arrows indicate the flow of blood to and from the heart, and 

 the flow of lymph always toward the heart and finally emptying into the blood, 

 in man mainly at the junction of left jugular and subclavian veins. (Reprinted from 

 The Machinery of the Human Body by Carlson and Johnson, by permission of 

 The University of Chicago Press. Copyright 1948.) 



