MOVEMENTS OF THE LYMPH AND THE CHYLE. 539 



and with it forms one of the important agents in the move- 

 ments of the lymph and chyle. 



These movements are studied with great difficulty. One 

 of the first peculiarities to be observed is, that under normal 

 conditions, the vessels are seldom distended ; and the quan- 

 tity of fluid which they contain is subject to considerable 

 variation. As far as the flow in the vessels of medium size 

 is concerned, the movement is probably continuous, subject 

 only to certain momentary obstructions or accelerations from 

 various causes. But in the large vessels situated near the 

 thorax, and in those within the chest, the movements are in 

 a marked degree remittent, or may even be intermittent. 

 All experimenters who have observed the flow of lymph or 

 chyle from a fistula into the thoracic duct have noted a con- 

 stant acceleration with each act of expiration ; and an im- 

 pulse synchronous with the pulsations of the heart has been 

 frequently observed. 



The fact that the lymphatic system is never distended, 

 and the existence of the numerous valves by which different 

 portions may become isolated, render it impossible to esti- 

 mate the general pressure of fluid in these vessels. This is 

 undoubtedly subject to great variations in the same vessels at 

 different times, and in different parts of the lymphatic sys- 

 tem. It is well known, for example, that the amount of dis- 

 tension of the thoracic duct is exceedingly variable, its capa- 

 city not infrequently being many times increased during 

 active absorption. At the same time it is difficult to attach 

 a manometer to any part of the lymphatic system without 

 seriously obstructing the circulation, and consequently ex- 

 aggerating the normal pressure. But the force with which 

 liquids penetrate these vessels is very great. This is illus- 

 trated by the experiment of ligating the thoracic duct ; for 

 after this operation, unless communicating vessels exist by 

 which the fluids can be discharged into the venous system, 

 their accumulation is frequently sufficient to rupture the 

 vessel. % 



