608 EXPERIMENTS DEALING WITH 



changes are observed in it : (a) The fluid rapidly decreases in 

 quantity owing to water being taken up by the blood. This goes 

 on until the osmotic pressure of the fluid left behind is raised to 

 that of the blood, (b) At the same time the soluble constituents 

 of the blood diffuse into the fluid, and the salt of the fluid into the 

 blood, until there is equal concentration of all diffusible substances- 

 on the two sides of the capillary wall. If the salt solution intro- 

 duced is hypertonic corresponding changes take place. If the 

 fluid is isotonic, only the changes under (b) will take place ; the 

 fluid will remain throughout isotonic, but will be different in com- 

 position from that introduced. 



Isotonic salt solutions are absorbed with rapidity from the 

 serous cavities, but the conditions of the experiment render it 

 impossible to decide finally whether they are absorbed only by 

 blood-vessels or by both blood-vessels and lymphatics. Large 

 quantities are absorbed without increasing the flow in the thoracic 

 duct ; but it is still possible, as Cohnstein maintained, that the 

 fluid has been taken up by the subserous lymphatics and so has 

 failed to reach the thoracic duct during the experiment. Starling 

 showed that ligature of both thoracic ducts and the right inno- 

 minate vein did not prevent absorption ; but, on the other hand, 

 that carmine injected with the solution could be traced to the 

 lymphatic glands in the anterior mediastinum, showing that fluid 

 had passed along lymphatics. It is probable, however, that in 

 the absorption of salt solutions the blood-vessels play the more 

 important part. 



It has been shown that absorption can take place independently 

 of the activity either of the endothelium lining the serous space 

 or of that forming the capillary wall. Leathes and Starling found 

 that scalding or killing the endothelium with a poisonous solution 

 of sodium fluoride did not affect absorption. Hamburger showed 

 that absorption took place from the abdomen of an animal twenty- 

 two hours after death. Although absorption can take place 

 independently of the activity of living cells, the explanation of 

 how it takes place at all is much less clear. 



Mechanism of the Absorption of Isotonic Salt Solutions. Starling 

 has pointed out that only two physical processes seem available for 

 explaining absorption backward filtration or osmosis with diffusion. 



Backward Filtration. The pressure under which tissue fluid 

 normally exists has been estimated by Landerer at from ^ to |- 



