208 



HUMAN PHYSIOLOGY 



as regards coagulation. The following table helps to explain 

 this (S. A. is Serum Albumin, S. G. Serum Globulin) : 



2. Formation of Lymph. Lymph is derived partly from 

 the blood and partly from the tissues. The formation of 

 lymph from the blood depends upon the permeability of the 

 walls of the capillaries and the pressure 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 are produced in the latter 

 apparently because of the small permeability of the limb 

 capillaries and the great permeability of the hepatic capil- 

 laries. The permeability may be increased by anything 

 which injures the capillary wall. Thus the injection of hot 

 water or of proteoses at once leads to an increased flow of 

 lymph. 



But, while the permeability of the vessel wall is the most 

 important factor controlling lymph formation, any increase 

 of the intra-vascular pressure of a region increases the flow 

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

 of blood from a part leads to increased lymph production. 



That lymph is also formed from the tissues is indicated 

 by the fact that the injection of substances of high osmotic 

 equivalent into the blood such as sugar or sulphate of soda 

 leads to a flow of fluid into the blood, so that it becomes 

 diluted, and also to an increased flow of lymph, and this in- 

 crease of water in both can be explained only by its withdrawal 

 from the tissues. 



