HEMOGLOBIN 137 



clot until a calcium salt is added. The oxalate does not interfere with gas 

 absorption and gas determination tests. 



Hirudin Plasma. Leach extract contains an anticoagulant which 

 prevents clotting of blood. Such blood clots readily on adding serum or 

 other solution containing thrombokinase which neutralizes the hirudin 

 effect as it does the antithrombin when blood is drawn. 



Peptone Plasma. Peptone solution injected directly into the blood 

 stream renders the blood non-coaguable when it is afterward drawn. 

 Peptone does not prevent blood from clotting when mixed in vitro. How- 

 ever, when blood serum or a pure solution of fibrin ferment is added, both of 

 which neutralize the antithrombin, then peptone plasma will form a clot. 



Water of Blood Plasma. The water of the plasma varies in amount 

 through a wide range. During absorption of food and drink the water 

 increases temporarily in the blood, though at this time it is flowing into 

 the tissues and being more rapidly excreted by the kidneys. In a few 

 minutes, say 15 or 20, after a glass of water the blood constituents will be 

 diluted and the red corpuscles demonstrably swollen. This condition 

 is quickly equalized. On the other hand the rapid loss of water in evapor- 

 ation of sweat following vigorous exercise quickly leads to loss of water 

 from and concentration of the plasma. These variations occur around an 

 average content of 90 per cent, of plasma water. 



Proteins. The chief proteins of plasma are serum albumin, serum 

 globulin, and fibrinogen, a total of from 6 to 8 per cent, of the plasma. 

 Fibrinogen is the part of plasma that is converted into fibrin when blood 

 clots. It is a globulin. Fibrinogen is precipitated from plasma by half 

 saturation with sodium chloride and along with globulin by full saturation 

 with sodium chloride or magnesium sulphate. It is soluble in dilute salt 

 solutions but not soluble in water. 



Serum globulin or paraglobulin is completely precipitated by saturation 

 by magnesium sulphate, incompletely by sodium chloride, and coagulates 

 at a temperature of 75 C. It is likewise soluble in dilute salt solutions, 

 but insoluble in water. It is present in plasma in from 3.5 to 4 per cent., 

 but varies greatly. 



Serum albumin is the protein which predominates in human plasma. 

 It is readily obtained in crystalline form ; is soluble in saturated magnesium 

 sulphate and sodium chloride solutions, but insoluble in saturated ammon- 

 ium sulphate solutions. It coagulates in neutral or acid solutions at from 



73 to 75 C. 



Extractives. The extractives are the nitrogen-containing substances, 

 such as urea, uric acid, creatin, creatinin, etc., and the non-nitrogenous 

 glycogen, dextrose, cholesterin, etc., a total of 0.5 to 0.6 per cent. The 

 dextrose content amounts to from o.i to 0.15 per cent. 



Among the extractives must be classed the various hydrolytic ferments 

 such as the diastatic ferments that react with the carbohydrates of the 



