340 ABSORPTION. 



muscles, peristaltic movements of the intestines, and pulsations of large arteries situ- 

 ated against the lymphatic trunks, particularly the thoracic aorta, are all capable of 

 increasing the rapidity of the circulation of the lymph and chyle. * 



The contractions of voluntary muscles assist the lymphatic circulation in precisely 

 the way in which they influence the flow of blood in the venous system; and we have 

 nothing to add regarding this action to what has already been said on this subject in 

 connection with the venous circulation. 



Increase in the flow of chyle in the thoracic duct, as the result of compression of the 

 abdominal organs or of kneading the abdomen with the hands, was observed by Magen- 

 die, and the fact has been confirmed in all recent experiments on this subject. The same 

 effect, though probably less in degree, is produced by the peristaltic contractions of the 

 intestines. 



When a tube is introduced into the upper part of the thoracic duct, it is frequently 

 the case that the fluid is discharged with increased force at each pulsation of the heart. 

 This was frequently observed by Dalton in his experiments on the thoracic duct, and he 

 describes the jets as being " like blood coming from a small artery when the circulation 

 is somewhat impeded." This impulse is due to compression of the thoracic duct as it 

 passes under the arch of the aorta. Its influence upon the general current of the lymph 

 and chyle is probably insignificant, but the fact attracted the attention of Haller, who 

 attached to it a great deal more importance than it is now believed to possess. 



Influence of the Movements of Respiration. While the vis a tergo must be regarded 

 as by far the most important agent in the production of the lymphatic circulation, the 

 movements of fluids in the thoracic duct receive constant and important aid from the 

 respiratory acts. This fact has long been recognized ; and in the works of Haller will 

 be found a full discussion of the influence of the diaphragm and of the movements of the 

 thorax upon the circulation of chyle. The observations of Colin on this subject are 

 most valuable, as he was the first to successfully establish a fistula into the thoracic duct 

 in large animals. He always found a marked remittency in the flow of chyle from a fis- 

 tula into the thoracic duct, which was absolutely synchronous with the movements of 

 respiration. With each act of expiration, the fluid was forcibly ejected, and, with inspira- 

 tion, the flow was very much diminished or even arrested. These impulses became much 

 more marked when respiration was interfered with and the efforts became violent. The 

 intermittency of the current was sometimes so decided, that the pulsations were repeated 

 in a long elastic tube attached to the canula for the purpose of collecting the fluid. 



The amount of influence exerted by the respiratory movements upon the flow of the 

 lymph and chyle can be best appreciated by examining carefully the mechanism of its 

 operation. 



With each act of inspiration, all the liquids, as well as the air, are drawn toward the 

 cavity of the thorax. In this way, the thoracic duct is dilated and then becomes most 

 distended with fluid. At the same time, the flow of lymph from the right lymphatic 

 duct into the right subclavian vein is increased. After the thoracic duct has been thus 

 dilated in inspiration, at the moment of expiration, in common with all the other parts 

 contained within the thorax, it undergoes compression ; the valves prevent the reflux of 

 its contents, and, as a necessary consequence, the fluid is then discharged with increased 

 force into the left subclavian vein. It can be readily understood how the act of inspira- 

 tion, while it has a tendency to fill the thoracic duct from below, opposes the discharge 

 of fluid from a fistula. 



From all these considerations, it is evident that, although there are many circum- 

 stances capable of modify ing the currents in the lymphatic system, the regular flow of the 

 lymph and chyle depends chiefly upon the vis a tergo ; but the vessels themselves some- 

 times undergo contraction, and they are subject to occasional compression from sur- 

 rounding parts, which, from the existence of numerous valves in the vessels, must favor 



