290 PROD UCTION AND ABSORPTION OF L YMPH. 



blood pressure below the obstruction. In spite of this fact, the lymph 

 flow from the thoracic duct may in some cases be unaltered and even 

 slightly increased. 



2. Obstruction of the inferior vena cava above the diaphragm causes 

 a general fall of blood pressure, and the intestines become apparently 

 anaemic. The lymph flow from the thoracic duct is largely increased, and 

 the lymph undergoes chemical changes, becoming more concentrated 

 than it was before the obstruction. This lymph, according to Heiden- 

 hain, comes from the intestines, whereas, on obstruction of the portal 

 vein, these organs yield an increased flow of a lymph which is less 

 concentrated than normal and contains red blood corpuscles. 



3. Heidenhain describes two classes of bodies, which on injection 

 into the circulation increase the lymph Jlow from the thoracic duct. 



The first class comprises bodies such as commercial peptone, watery 

 extract of dried leeches or of crayfish. These increase the lymph and 

 make it more concentrated. They usually cause a lowering of arterial 

 blood pressure, although by careful injection this may be avoided. 



The second class includes crystalloids such as sodium chloride, sugar, 

 etc. Injection of concentrated solutions of these bodies into the circula- 

 tion evokes an increased flow of lymph which is less concentrated than 

 before. Some time after the injection, it is found that the lymph 

 contains a greater percentage amount of injected substance than does 

 the blood plasma. There may be a slight rise in the arterial pressure, 

 but this rise is in no way proportionate to the augmentation in the 

 lymph flow. 



Since, therefore, the lymph flow may be increased without any 

 corresponding elevation in the blood pressure, and since the amount of 

 injected substance in the lymph may rise above that in the blood plasma, 

 Heidenhain concludes that the processes of filtration and diffusion are 

 incapable of accounting for the changes observed in the amount and 

 composition of the lymph ; although he does not deny that, under certain 

 pathological conditions, such as heart disease and cirrhosis of the liver, 

 dropsy or ascites may be and probably is conditioned by the increased 

 intracapillary pressure acting in many cases on a capillary wall already 

 weakened and abnormal in consequence of amemic and diseased states 

 of the blood. 



Comparison of the theories of Ludwig and Heidenhain. A 

 renewed examination 1 of Heidenhain's experiments, combined with a 

 more thorough investigation of their conditions, has persuaded me that, 

 so far from overthrowing the filtration hypothesis, they furnish the 

 strongest arguments which have yet been adduced in its favour. I may 

 therefore give some account of these experiments, and show how they 

 support Ludwig's contention with regard to the production of lymph. 



Sources of the lymph investigated. In dealing with the lymph flow 

 from the thoracic duct, it is essential to know from what parts of the 

 body this lymph is derived, especially since, as is well known, the 

 lymphatics from all parts of the body, with the exception of the 

 right upper extremity and right side of the neck, converge to pour 

 their contents into this duct. In placing a cannula in the duct, 

 in order to collect and measure the lymph, the ducts from the left 

 side of the neck and left upper extremity are ligatured. From the 



1 Bayliss and Starling, Journ. PhysioL, Cambridge and London, vol. xvi. p. 159 ; Star- 

 ling, ibid. vol. xvi. p. 224, and vol. xvii. p. 30. 



