LYMPH FORMATION 597 



(3) Obstruction of the inferior vena cava between the heart 

 and hepatic veins causes a great fall of arterial pressure, the in- 

 testines becoming blanched. The lymph flow is increased ten 

 to twenty times, and contains the same increased percentage of 

 proteids as in the previous experiment. 



Starling showed that the same fallacy as before underlay 

 Heidenhain's interpretation of the result. The pressure in the 

 aorta may fall to a third, but that in the portal vein and inferior 

 vena cava is considerably increased. The capillary pressure in 

 the intestines is probably decreased on the whole, but that in the 

 liver must be increased three to four times. Ligature of the liver 

 lymphatics stops all flow along the thoracic duct in this ex- 

 periment. 



(4) Injection of any of Heidenhain's second class of lympha- 

 gogues, which includes various crystalloids, such as sugar, urea, 

 salts, &c. The injection of these in concentrated solution causes 

 .an enormously increased flow of less concentrated lymph and a 

 more watery condition of the blood. The arterial pressure may 

 be slightly increased, but it is not proportional to the lymph 

 flow. 



Heidenhain rejected a physical explanation of the action of 

 these substances, in spite of the fact that the increase in lymph 

 flow was known to be proportional to the osmotic pressure of the 

 solution used. The physical explanation he himself proposed and 

 rejected was that the injected crystalloid rapidly diffused into the 

 tissue spaces and attracted fluid there from the tissue cells and 

 fibres. His reason for rejecting it was his observation that directly 

 after the injection was over the percentage of the lymphagogue 

 began to fall in the blood and rise in the lymph, until the lymph 

 contained a greater percentage than the blood. This condition of 

 things he considered incompatible with diffusion, and only cap- 

 able of explanation by the secretion of the crystalloid into the 

 lymph by the capillary walls. 



Leathes had shown that the injection of such solutions in- 

 creased the volume of the circulating blood by attracting fluid into 

 it in other words, caused a condition of hydrsemic plethora. 

 Starling demonstrated the influence of this condition on capillary 

 blood pressure by measuring the pressures in the aorta, the portal 

 vein, and inferior vena cava simultaneously. He found that while 

 the aortic pressure was but little increased, there was a marked 



