596 EXPERIMENTS DEALING WITH 



his results by filtration and diffusion. He therefore assumed the 

 intervention of the vital activity of cells, and put forward the view 

 that lymph is secreted by the cells of the capillary wall. This 

 secretory activity is aided by physical forces, but can and does 

 override them. He further considered that he had shown that 

 this secretion could be stimulated by chemical substances intro- 

 duced into the blood, and suggested that in the body the products 

 of cell katabolism had a similar lymphagogue action. He also 

 suggested that the secretion might be under the direct control of 

 the nervous system. 



The experiments on which Heidenhain relied to show that 

 blood pressure and lymph flow do not run parallel have been 

 repeated by Starling, and, although the results have been con- 

 firmed, it has been shown that they are open "to explanation 

 on Ludwig's theory. Heidenhain's more important experiments 

 were : 



(1) Ligature of the portal vein. This increased the lymph 

 flow four to five times ; the lymph contains less proteid per 

 cent, than normal and is blood-stained. This result is obviously 

 capable of explanation on the filtration theory, as due to an 

 increased capillary pressure causing increased filtration and a 

 decreased concentration of proteid in the filtrate. 



(2) Obstruction of the thoracic aorta causes a great fall of 

 blood pressure below the obstruction. The lymph flow is gener- 

 ally decreased, but may be unaltered or slightly increased, but in 

 all cases the percentage of proteid is increased. 



Starling pointed out that since Heidenhain considered change 

 only in the arterial and not in the venous pressures, it was im- 

 possible for him to deduce the change in the capillary pressures. 

 He showed that pressure in the portal vein falls greatly, but in the 

 inferior vena cava is unaltered or slightly increased. Therefore 

 the pressure in the intestinal capillaries is very far below normal, 

 but in the liver capillaries is either unaltered or slightly increased. 

 By ligaturing the hepatic lymphatics he stopped the flow along the 

 thoracic duct absolutely, showing that in this experiment all the 

 lymph was coming from the liver. By this and other experiments 

 he demonstrated that the lymph in the thoracic duct is a 

 mixture of two fluids, one with a high percentage of proteid 

 coming from the liver and the other with a less percentage from 

 the intestines. 



