40 THE BLOOD 



cubic millimeter of blood. As to their function little is known. 

 Some claim they play an important part in the coagulation of the 

 blood. Nothing definite is known of their origin. 



The Coagulation of the Blood. 



When blood is allowed to stand after being shed it rapidly 

 becomes more viscous and later sets into a firm jelly. Later, 

 as the fibrin contracts, a clear straw colored fluid, the serum, is 

 set free. The formation of fibrin is the essential factor in 

 coagulation. It is contained in the plasma in the form of 

 fibrinogen. 



The relation of plasma, serum and clot is shown by the fol- 

 lowing table: 



( Serum 

 Plasma < _., . ^ 



Corpuscles J 



