FORMATION OF LYMPH 29 



Under normal conditions, according to Starling, lymph 

 formation is influenced by two factors^ — the state of the 

 blood and the state of the tissue. As to the blood, the 

 lymph is exuded from it owing to the capillary pressure. 

 When this increases, other things being equal, the amount 

 of lymph formed increases also. In confirmation of this, 

 Starling found that the rate of lymph flow from the hver 

 was increased when the venous outflow was obstructed, and 

 diminished when the arterial supply was lowered. It can, 

 however, be argued that this efiect is produced indirectly 

 by the altered metabohsm due to the stagnation of the blood. 

 It is known that deficient oxygenation causes an excessive 

 flow of fluid into the tissue spaces (CEdema), 



But the effect of blood pressure is partly counterbalanced 

 by the osmotic pressure of the plasma colloids, which pass 

 but slowly through the capillary walls. The importance 

 of the osmotic pressure of the plasma proteins as a factor 

 in restraining the passage of fluid from the blood is shown 

 by the therapeutic effect of infusions for severe haemorrhage. 

 It is now agreed that isotonic sahne is of little use for this 

 purpose, since, owing to the dilution of the plasma proteins, 

 capillary pressure exceeds osmotic pressure, so that all 

 the fluid injected passes into the tissues. To be retained, the 

 injecting fluid must have an osmotic pressure equal to that 

 of plasma. To this end a 6 per cent, solution of gum arable 

 is used. The effective force driving the lymph out of the 

 capillaries is therefore the capillary pressure minus the differ- 

 ence between the osmotic pressure of the plasma proteins and 

 the osmotic pressure of the lymph proteins. 



But while this force drives the lymph a tergo, another 

 draws it a fronte. This is the activity of the tissue-cells. 

 In every tissue lymph-formation increases with activity. 

 In the hmbs lymph only flows when the muscles are working. 

 Starhng explains the coincidence of lymph-flow with 

 activity in this way. When the cells become active, large 

 molecules are broken down into smaller ones. The osmotic 

 pressure within the cells and tissue-spaces is thus raised. 



