CHEMISTRY OF BLOOD 163 



through and through the mass of blood which makes it retain the form of 

 the vessel when undisturbed clotting occurs. 



e. The Influence of Salt Solution on Blood Clotting. Add 2 cc.of saturated 

 magnesium sulphate, i per cent, sodium oxalate, and 0.9 per cent, sodium 

 chloride to each of three test-tubes. Draw into each test-tube 5 to 6 cc. of 

 blood and immediately mix thoroughly and let stand. The magnesium 

 and oxalate test-tubes will not coagulate even though -they stand for days, 

 but the sodium-chloride blood will clot in a few minutes. 



The magnesium-sulphate blood will coagulate if diluted with a sufficient 

 amount of distilled water or physiological saline solution. Make a series 

 of dilutions and note when coagulation takes place. The sodium-oxalate 

 blood will coagulate when a sufficient excess (of i per cent, solution) of 

 calcium chloride is carefully added to neutralize the excess of sodium 

 oxalate. Demonstrate these on a series of samples. 



If a quantity of magnesium or oxalate blood is secured and separated by 

 a centrifuge or by letting stand for a sufficient time, a sample of uncoagulated 

 plasma will be obtained. This sample will coagulate when it is treated as 

 just described above for blood, showing that the antecedents of fibrin are 

 found in the plasma. 



/. Action of Tissue Extracts on Coagulation. Wash out the blood of 

 a small animal by circulating 0.9 per cent, saline through the arteries until 

 the outflowing fluid from the veins is clear. Take an organ, the liver for 

 example, grind it up in a sausage mill by running it through the mill two 

 or three times, then extract with 0.9 per cent, physiological saline. The 

 macerating mass should be shaken up at intervals, and may be kept from 

 spoiling by adding an excess of chloroform or by keeping on ice. A few 

 cubic centimeters of this fluid extract added to a sample of freshly drawn 

 blood will very greatly hasten the rapidity of coagulation. This tissue ex- 

 tract contains the thrombqplastin of Howell (Thrombokinase of Morawitz), 

 and hastens the formation of thrombin from thrombogen. 



ii. The Chemistry of Blood Plasma (or Serum). The blood plasma 

 contains all the chemical substances which are utilized by the tissues in 

 their nutrition or which are thrown off by the tissues as a result of their 

 activity. It is therefore a very complex mixture. The serum contains the 

 same substances in the same proportion, with the exception of the antece- 

 dents of fibrin. It may, therefore, be used as a substitute for plasma in 

 most cases. 



a. Proteins of Plasma. There are three principal proteins in blood 

 plasma: serum-albumin, serum-globulin, and fibrinogen. These may be 

 isolated as follows: To a sample of blood plasma add an equal quantity of 

 sodium-chloride solution that has been saturated at 40 C. A white floccu- 

 lent precipitate of fibrinogen comes down. Filter off, and add to the filtrate 



