VASOMOTOR SUPPLY OF THE ORGANS. 631 



the pressure in the hquid of the surrounding tissues must also be consider- 

 able. The tissues are, in fact, in a condition of turgidity owing to the 

 pressure of the lymph in the tissue-spaces. This difference in pressure 

 at the two ends of the lymphatic system is the main constant factor in mov- 

 ing the lymph. It is obvious that in the long run it is dependent upon the 

 pressure within the blood-vessels and therefere upon the force of the heart 

 beat. The contractions of the heart supply the energy, not only for the move- 

 ment of the blood, but also for the much slower movement of the lymph. The 

 circulation of the lymph is aided, however, by many accessory factors. In 

 some animals there are genuine lymph hearts upon the course of the vessels, — 

 that is, pulsatile expansions of the lymph vessels whose force of beat, con- 

 trolled by valves, is directly applied to moving the lymph. No such structures 

 are found in the mammalia, but according to some observers the large re- 

 ceptacle at the beginning of the thoracic duct, receptaculum chyli may 

 midergo contractions, and is, besides, imder the influence of motor and 

 inhibitory nerves. Such movements, if they occur, must be equivalent to the 

 action of a lymph heart in their influence upon the flow of lymph. The 

 flow of lymph or chyle in the intestinal area is also, without doubt, greatly 

 assisted by the peristaltic and especially by the rhythmic contractions of the 

 musculature of the intestines, and by the independent movements of the 

 villi. The volume of the lymph in this region is especially large and the 

 lymph capillaries and veins are provided with valves. Rhythmical ccm- 

 tractions of the musculature of the intestine must squeeze the lymph toward 

 the thoracic duct, acting like a local pump to accelerate the flow of lymph. 

 A similar influence is exerted by the contractions of the skeletal muscles. The 

 compression exerted by the shortened fibers squeezes the lymph vessels and, 

 on account of the valves present, forces the lymph onward toward the larger 

 ducts. The flow of lymph from the resting muscles — the arms and legs, for 

 instance — is normally small in quantity, but during muscular exercise and 

 massage it is obviously increased. This increase may be observed in experi- 

 mental work by placing a cannula in the thoracic duct. Active or passive 

 movements of the limbs under these conditions will cause a noticeable increase 

 in the outflow from the duct. Still another factor which exercises an in- 

 fluence upon the flow of the lymph is found in the respiratory movements of 

 the thorax. At each inspiration the pressure within the thorax is dimin- 

 ished (increase of negative pressure), and this factor influences the lymph 

 flow in several ways: By increasing the flow of blood through the large veins 

 at the edge of the thorax, jugulars, and subclavians, it doubtless aspirates 

 lymph from the thoracic and right lymphatic ducts into these veins. More- 

 over, by lowering the pre-ssure upon the intrathoracic portion of the thoracic 

 duct it also aspirates the lymph from the abdominal portion of this vessel. 



When we place a cannula in the thoracic duct and measure the outflow 

 directly it is found to be exceedingly slow and variable. Older measure- 

 ments (Weiss) indicate that it has a velocity in the duct in the neck of about 

 4 mms. per second, but this velocity changes naturally with the conditions 

 influencing the production of lymph in the tissues. After meals, during the 

 period of absorption from the alimentary canal, the flow is much more abun- 

 dant than in the fasting animal. Heidenhain estimates that for a dog weighing 

 10 kgms. the total outflow from the thoracic duct in twenty-four hours is equal 

 to 640 c.c. Munk and Rosenstein, from observations upon a case with a 

 lymph fistula, estimated that in man the flow may be equal to 50 to 100 or 120 

 c.c. per hour. 



