292 THE BLOOD 



salts ; and of these, sodium chlorid is the most abundant, being 

 present to the amount of 0.55 per cent. Sodium carbonate is 

 present to the amount of 0.15 per cent. ; and this salt is the 

 principal cause of the alkalinity of the plasma, and gives it its 

 power to absorb carbon dioxid. The salts of the plasma have not 

 been exactly determined, but, according to Schmidt, the following 

 table gives those that probably occur, with their percentages : 



Potassium sulphate 0.0281 



Potassium chlorid 0.0359 



Sodium chlorid 0.5546 



Sodium phosphate 0.0271 



Sodium carbonate 0.1532 



Calcium phosphate 0298 



Magnesium phosphate 0.0218 



Calcium chlorid is probably also present, and traces of a 

 fluorid have likewise been found. 



Extractives. These include carbohydrates, of which there are 

 three : Glycogen, probably derived from the leukocytes ; an 

 animal gum; and dextrose. This last, we have seen, is always 

 present in human blood to the amount of about 0.12 per cent., 

 being much more abundant in portal blood during the digestion 

 of carbohydrates. Fat is also a constituent of the plasma, the 

 amount being increased by its absorption after a meal containing 

 it. Lecithin, cholesterin, lipochrome (which gives the plasma its 

 yellow color), urea, uric acid, kreatin, kreatinin, and occasionally 

 hippuric acid are also present. 



Enzymes. Plasma contains at least five enzymes : (1) An amyl- 

 olytic, which is, according to some authorities, produced by the red 

 cells, while others attribute it to the leukocytes ; (2) a glycolytic, 

 causing a destruction of some of the dextrose in the blood. Al- 

 though the existence of this enzyme is denied, there is strong evi- 

 dence in favor of its existence. According to Spitzer, it exists in 

 both red and white blood-cells and, indeed, in all tissue-cells. It 

 acts only in the presence of oxygen ; (3) a lipolytic, called lipase; 

 (4) a coagulating thrombin or prothrombin, which causes coagula- 

 tion of the blood under some circumstances (p. 293) ; (5) a proteolytic. 

 The destruction of the exudate of pneumonia is attributed to this 

 enzyme. 



Proteids. These are : (1) Serum-albumins, a, ft, and y (p. 108) ; 

 (2) serum-globulin or paraglobulin (p. 110); (3) fibrinogen (p. 

 110) ; (4) nucleoproteid. 



The total proteids in human plasma are 7.62 per cent., of 

 which 3.10 per cent, are globulins, and 4.52 per cent, albumins. 



The proteids of the plasma have been already discussed in 

 dealing with this class of physiologic ingredients (p. 126), but 

 one of them, fibrinogen, deserves special notice at this time because 

 of its relation to the process of blood-coagulation. 



