440 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Fibrinogen is precipitated by adding an equal volume of saturated sodium 

 chloride solution. The precipitate is filtered off, washed with half-saturated 

 sodium chloride solution, dissolved in water and reprecipitated. 



(b) From magnesium sulphate plasma. 



Fibrinogen is precipitated by adding an equal volume of saturated 

 sodium chloride solution to magnesium sulphate plasma. The precipitate 

 is filtered off and washed with half- saturated sodium chloride solution. It is 

 purified by dissolving in water and reprecipitating with sodium sulphate. 



!c) From oxalate plasma, 

 i) The fibrinogen is precipitated by adding an equal volume of saturated 

 sodium chloride solution (Ca-free). It is filtered off and washed with half- 

 saturated sodium chloride solution, redissolved and reprecipitated. 



(ii) The fibrinogen is precipitated by quarter-saturation with am- 

 monium sulphate. Every 12 c.c. of oxalate plasma are diluted with 

 30 c.c. of water and 20 c.c. of saturated ammonium sulphate are added. 

 The precipitate is filtered ofT, washed with quarter-saturated ammonium 

 sulphate, dissolved in water and reprecipitated. 



Fibrinogen gives the colour reactions, coagulation reactions and 

 precipitation reactions of proteins. 



It is a globulin, being soluble in dilute salt solutions but insoluble 

 in water. It is precipitated from solution by salts, but less than com- 

 plete saturation (half-saturation) with sodium chloride and less than 

 half-saturation (quarter-saturation) with ammonium sulphate throws it 

 out of solution. It is, therefore, an atypical globulin. 



Its temperature of heat coagulation in a dilute salt solution is 56. 



It is converted into insoluble fibrin by thrombin : 



(a) Fibrinogen from Sodium Sulphate Plasma. 



The fibrinogen on solution in water, 1 if it has been well washed, will not 

 clot if kept at 40 for 10-15 minutes, but it is converted into fibrin if a 

 little serum or fibrin ferment solution be added. 



(b) Fibrinogen from Magnesium Sulphate Plasma. 



A solution of the well-washed fibrinogen in water J does not clot on warming 

 to 40, but it gives fibrin if a drop of serum or thrombin solution be added. 



(c) Fibrinogen from Oxalate Plasma. 



A solution of fibrinogen in water 1 may clot at 40 on adding calcium 

 chloride as it will be contaminated with thrombokinase and thrombogen. 



It is converted into fibrin if a drop of serum or thrombin solution 

 be added. 



Fibrin. 



Fibrin is not usually prepared from fibrinogen, but directly from 

 blood. The blood, when drawn, is immediately whipped with a 

 bundle of twigs. Threads of fibrin collect on the twigs ; they are re- 

 moved, placed in a muslin bag and washed with running water. 



1 It dissolves in water as sufficient salt is still present with it. 



