LYMPH 509 



explain it. The most careful study seems to show that 

 these physical factors are adequate and that filtration plays 

 the most prominent part. 



(1) The formation of lymph from the blood depends largely 

 upon the permeability of the ivalls of the capillaries and 

 the p)'^'^ss^ire of blood in the blood-vessels. Thus, although 

 the pressure in the blood-vessels of the limbs is much higher 

 than the pressure in the vessels of the liver, hardly any 

 lymph is usually produced in the former, while very large 

 quantities containing a high percentage of proteins are 

 produced in the latter — apparently because of the slight 

 permeability of the limb capillaries and the great permeability 

 of the hepatic capillaries. The permeability may be increased 

 bv the injection of hot water or of proteoses, probably because 

 these injure the capillary walls, but possibly because they 

 increase the activity of the organ. 



While the permeability of the vessel wall is the most 

 important factor controlling lymph formation, any increase 

 of the intravasculo.r pressure of a region ma}" increase the 

 flow of lymph, and for this reason any obstruction to the 

 free flow of blood from a part leads to increased lymph 

 production from that area. 



Asher has pointed out that the flow of lymph from 

 the salivary glands and from the liver is increased with the 

 increased activity of the organ irrespective of changes in 

 blood pressure. Even after death, the flow of lymph may 

 go on. He explains this by supposing that the activity of a 

 Sfland leads to the breaking down of larger into smaller 

 molecules, which increases the osmotic pressure of the fluid 

 in the lymph spaces and thus causes an osmosis of water and 

 an increased lymph formation. After death the disintegra- 

 tive changes may produce these smaller molecules and 

 have the same eftect. 



A method of washing out wounds by causing a flow of 

 lymph has been based upon this action of osmosis. The 

 application to the w^ound of a hypertonic saline brings it 

 about. 



(2) That lymph is also formed from the tissues is indicated 

 by the fact that the injection of substances of high osmotic 



