26 BLOOD 



thrombin must be credited to the sahvary glands of the 

 leech. 



The process of coagulation may be tabulated thus — 



Prothrombin 

 (in plasma) 

 in presence of Ca 

 and of thrombo- 

 kinase (in all 

 tissues and plate- 

 lets). 



Thrombin + Fibrinogen 

 I (in plasma). 



Fibrin + Corpuscles. 



I 



Clot. 



THE LYMPHATIC SYSTEM 



In all parts of the body, with the exception of the spleen- 

 pulp, the tissue-cells are bathed in a fluid — the lymph (Fig, 

 3). This is contained in irregular spaces separating the cells 

 from one another, and from the walls of the blood-capillaries. 

 Through the lymph nutritive substances pass from the 

 blood to the cells, and waste-products pass from the cells 

 to the blood. 



Lymph originates in the blood-plasma. It is continually 

 passing in and out through the capillary walls. A certain 

 amount, however, regains the blood indirectly by a system 

 of vessels — the lymphatics — comparable in structure to 

 the veins. Lymph-capillaries originate in the intercellular 

 spaces and join together to form larger vessels which again 

 unite to form on each side a duct which drains into the 

 blood at the junction of the subclavian and jugular veins. 

 The two ducts are very unequal in size and in the territory 

 from which they gain tributaries. That on the left is much 



