PHYSIOLOGIC IMPORTANCE OF LYMPH 



I ul, ; 



nels and the resultant increased intralymphatic 

 pressure and distention of the lymph vessels might 

 conceivably permit leakage of substances which 

 ordinarily would be retained within the lymphatic 

 vessels as has been previously shown to be true in 

 earlier work cited above. This has been shown to be true 

 of blood capillaries (197). Furthermore, the fact that 

 Courtice and Steinbeck found no protein leakage when 

 the ducts were not ligated suggests that the lymphatics 

 of the anterior mediastinum, under normal circum- 

 stances, will not permit leakage of significant amounts 

 of the protein which is contained by them. 



In a recent study (168) we attempted to obtain 

 answers to the questions: a) Does the capillary filtrate, 

 once it is in the lymph ducts, empty without loss into 

 the venous circulation or is protein free to pass out 

 of the lymphatic vessels throughout their lengths? 



b) Does any protein pass into the blood capillaries? 



c) Is any considerable amount of protein phagocytized 

 by the reticuloendothelial cells of lymph nodes? 

 Furthermore, to what degree, if any, is lymph 

 shunted to the blood stream through lymph-blood 

 anastomoses without returning via the thoracic 

 duct? Anomalous shunts, consisting of multiple 

 outlets of right and left ducts, have been described 

 as well as shunts between the right and left thoracic 

 ducts in about 15 per cent of dogs (234, 197). One 

 phase of our study involves the cannulation of a leg 

 lymphatic in an anesthetized dog, the infusion into it 

 of substances of different molecular weights, and 

 obtaining and analyzing samples of thoracic duct 

 lymph and plasma. The infused material thus travels 

 through a number of lymph nodes, through lymphatic 

 vessels of different sizes, and through capillaries. 



The second approach to the problem is to utilize a 

 preparation developed some years ago by Drinker 

 and his group (63). One afferent and one efferent 

 duct going to and from the popliteal node are isolated 

 and catheterized with polyethylene tubing. All other 

 lymphatics are tied off. Test substances are infused 

 through the node from the afferent side and collec- 

 tions are made on the efferent side. Nodal and systemic 

 plasma are also obtained and analyzed. 



When radioactive iodinated albumin is infused into 

 a leg lymphatic, there is a typical, consistent pattern 

 of appearance of the albumin in thoracic duct lvmph 

 as shown in figure 5. There is a lag time of approxi- 

 mately 10 min between the start of the infusion into 

 the leg lymphatic and the appearance of measurable 

 amounts of radioactive albumin in thoracic duct 

 lymph. This is followed by an abrupt rise to a plateau 

 which is maintained at an approximately constant 



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100 



50 



50 



100 



150 



fig. 5. Concentration of dextran and I 131 albumin in lymph 

 and plasma. Dextran and I 131 albumin solutions infused cen- 

 trally into leg lymphatic of anesthetized dog at zero time at 

 rate of 0.5 ml/min. Infusions of dextran and albumin stopped 

 after 50 min and 0.9% saline infusion started at same rate for 

 next 1 00 min. All values are corrected for free iodine. 



level for the 50-min duration of the albumin infusion 

 and for 10 min of a subsequent saline infusion. At 

 this time, radioactivity in thoracic duct lymph falls 

 sharply and continues to fall until the level approxi- 

 mates zero in about 140 to 150 min. Plasma radio- 

 activity rises to a maximum concentration after 60 to 

 90 min and remains at this level for the remainder 

 of the experiment. The maximum plasma concentra- 

 tion is less than 0.00 1 of the thoracic duct lymph 

 concentration during its 50-min plateau period. 

 Figure 5 also shows the similar behavior of dextran of 

 approximately the same average molecular weight 

 as albumin. It is apparent that these infused sub- 

 stances do not leave the lymphatic system and that 

 they return to the circulation primarily by the 

 thoracic duct. Actually less than 3 per cent of the 

 infused material reaches the circulation by routes 

 other than the thoracic duct, except in unusual cases 

 of right and left duct anastomoses. The experiments 



