Lymph 



THE LYMPH AND ITS MOVEMENT 71 



other, requires a word of explanation. As a matter of fact, it is im- 

 possible for the lymph to flow into blood vessels at most places on 

 account of the blood pressure. This would 

 force the blood into the lymph vessels, 

 instead of allowing the lymph to enter the 

 blood. The lymph can enter only at some 

 place where the blood pressure is less than 

 the pressure that moves the lymph. Such 

 a place is found in the thoracic cavity. As 

 already pointed out (page 54), the blood 

 pressure in the veins entering this cavity 

 becomes, with each expansion of the chest, 

 negative, i.e., less than the pressure of the 

 atmosphere on the outside of the body. 

 This, as we have seen, aids in the flow 

 of the blood into the right auricle. It also 

 'Gland aids in the passage of lymph into the 

 blood vessels. The lymph is said to be 

 " sucked in," which means that it is forced 

 in by the unbalanced pressure of the 

 atmosphere. 1 Some advantage is also 

 gained by the lymph 

 duct's entering the 

 Capillary subclavian vein on 

 the upper side and 

 at its union with the 

 jugular vein. Every- 



FIG. 30. Diagram showing gen- thing considered, it 



eral movement of lymph from the place SSjSgljX [ s found that the 

 of relatively high pressure at the lymph S~ lymph flows into 



spaces to the place of relatively low T the blood vessels 



pressure in the thoracic cavity. where j t can be 



" drawn in " by the movements of breathing and where it meets with no 

 opposition from the blood stream itself (Fig. 30). 



Lymph Movements at the Cells. The double move- 

 ment of the lymph from the capillaries toward the cells 



Lymphatic 

 lube 



1 Surgeons in opening veins near the thoracic cavity have to be on their guard to 

 prevent air from being sucked into them, thereby causing death. 



