6 4 



HUMAN BIOLOGY 



under the collar bones, near the neck. The one that empties under the 

 left collar bone (3, Fig. 66) is called the thoracic duct because it goes 



FIG. 64. SURFACE LYMPHATICS OF HAND. 



up through the thorax just in front of the spinal column (i. Fig. 66). 

 The other at the right side of the neck is called the right lymphatic 

 duct (see Figs. 64, 65). 



In persons with the dropsy, the lymph accumulates in the lymph 

 spaces and is not drained away by the lymph flow. Dropsy usually 



shows itself first by swelling of the feet and 

 the leg below the knee. (Why ? See Exp. 2.) 

 There is a set of lymphatics called lacteals, 

 situated in the abdomen, which have the func- 

 tion of absorbing digested fats from the intes- 

 tine (Figs. 66, 100, and colored figure 2). 



What makes the Lymph Flow ? - - The heart 

 does not, for its pressure is not transmitted be- 

 yond the blood tubes. The successive pressures 

 of a working muscle move the lymph forward 

 in the lymphatics in the same way that the blood 

 is moved forward in the veins, and the valves 

 keep it from moving back. When riding a trot- 

 ting horse, or in a jolting vehicle, the lymph is 

 moved beyond the valves at every jolt (Fig. 

 64). Without exercise the lymph stagnates, 

 and the body becomes poisoned by its own 

 wastes. At every expansion of the lungs lymph 

 is drawn into the chest ; and it is forced out of the chest at every con- 

 traction. Deep breathing is as great a benefit to the body in moving 

 stagnant lymph as it is in purifying the blood. 



B'IG. 65. DIAGRAM TO 

 SHOW THE Two 

 PARTS OF THE BODY 

 DRAINED BY THE 

 Two LYMPH DUCTS. 



