LYMPH ABSORPTION 613 



the actual proteids in serum do not exert an osmotic pressure, 

 but lie admits that serum contains something to which gelatine 

 and parchment are impermeable and gives a readable osmotic 

 pressure. His observations, therefore, do not render Starling's 

 view untenable. 



The Absorption of Serum. Starling carried on an artificial 

 circulation of defibrinated blood through a dog's leg, made 

 oedematous with the same serum, but was unable to demonstrate 

 any absorption by blood-vessels. But serum is absorbed from 

 serous cavities, although it takes place more slowly than in the 

 case of isotonic salt solutions. If this absorption of proteids 

 took place by blood-vessels it could only be accounted for either 

 by invoking a secretory activity by the endothelium or by 

 backward nitration, a phenomenon which has not as yet been 

 demonstrated, although Hamburger, Adler, and Meltzer found that 

 moderate pressure does increase the rate at which fluid disappears 

 from the abdominal cavity. Differences in osmotic pressure could 

 not carry proteid through the impermeable capillary wall. 

 Absorption of serum by blood-vessels might be possible to a 

 small extent, according to Starling, by tissue cell eating up the 

 proteid and a corresponding absorption of isotonic fluid taking 

 place. But practically, on a mechanical view of absorption, it 

 is necessary to believe that serum is carried away by the 

 lymphatics. Attempts have been made to show that this is not 

 the case. Orlow found that ligature of the thoracic duct did 

 not prevent absorption from the abdominal cavity, and Hamburger 

 obtained the same result after ligaturing the left innominate 

 vein. These experiments are inconclusive, because the right 

 thoracic duct was unligatured, and the fluid might have passed 

 into the subserous lymphatics, a point which has already been 

 dealt with in discussing the absorption of salt solutions. 



Physical Factors available for the Production and Absorption of 

 Tissue Fluid. We have seen that the following factors have been 

 considered to be available for explaining the experimental results 

 dealing with lymph formation and absorption. 



1. The intracapillary blood pressure P. 



2. The pressure of the tissue fluid p. 



P p constitutes the filtering force, p P a possible fcrce of 

 backward filtration. 1 



1 See Editor's note, p. 618. 



