28 BLOOD 



minute. The rate of flow from any tissue varies with physio- 

 logical activity. When the body is at rest there is practically 

 no flow from the Hmbs, all the lymph being derived from 

 the viscera, particularly the liver. 



Properties of Lymph 



Lymph is usually a clear, alkahne fluid which clots slowly 

 on standing. It contains the same saline constituents 

 as blood plasma. Its protein content varies with its origin, 

 being much higher in lymph which comes from the viscera 

 than in that which is derived from the limbs. Normal 

 lymph always contains less protein than blood. The lymph 

 which comes from the intestine is known as chyle. During 

 digestion it is milky, due to fat held in suspension. 



The Formation of Lymph 



Whether lymph is formed by a physical process or by 

 secretion is an old controversy. Heidenhain argued that 

 it was due to secretion. He discovered that there were 

 certain substances which increased lymph formation. These 

 he called lymfhagogues. He divided them into two classes 

 — the first class consisting of protein substances — 

 such as peptones, mussel-extract; the second class con- 

 sisting of crystalloid bodies such as dextrose and urea. 

 Both these classes owed their effect, Heidenhain believed, 

 to a stimulating action upon the secretory process. 



Foremost amongst the opponents of this view is Starling. 

 According to Starling, the action of the first class of 

 lymphagogues can be discounted because these substances 

 are toxic. The action of the second class is due to a dis- 

 turbance of osmotic relations. When these substances 

 are injected they raise the osmotic pressure of the blood 

 and thus cause withdrawal of water from the lymph-spaces 

 into the blood. As they themselves, being slightly diffusible, 

 pass into the lymph-spaces they cause a flow by osmosis 

 in the opposite direction — in this way causing an increased 

 flow of lymph. 



