1 66 ESSENTIALS OF PHYSIOLOGY. 



On analysis, plasma is found to contain a large number of sub- 

 stances, some of which, particularly fibrinogen, appear to be essential 

 constituents of the plasma itself, some are food stuffs being conveyed 

 to the tissues, some are waste products being carried to excretory 

 organs, and others are hormones, enzymes, and bodies of like nature. 

 A list of the principal constituents is given in the following table : 



The Composition of Blood Plasma. 



Water, 92 per cent. 



Proteins serum albumin, serum globulin, fibrinogen 6 to 8 per cent. 



Dextrose, 0'15 per cent. 



Neutral fats. 



Urea (0*02 to O05 per cent.), lecithin, cholesterol, lactic acid, and 

 other bodies. 



Hormones. 



Enzymes lipase, etc. 



Inorganic salts chlorides, sulphates, phosphates, and carbonates of 

 sodium, potassium, calcium, magnesium, and iron. 



Pigment and aromatic substances. 



Gases oxygen, carbonic acid, and nitrogen. 



The Proteins of Plasma. If an equal volume of a saturated solution 

 of sodium chloride is added to plasma, and the mixture is allowed to 

 stand, a sticky white precipitate separates out, consisting of fibrinogen. 

 This substance is a globulin, and the precipitate may be dissolved in 

 weak salt solution. Fibrinogen exists in much smaller quantity than 

 the other proteins, forming about 0*3 per cent, of the plasma. If 

 plasma is allowed to clot, a comparatively insoluble, stringy substance 

 called fibrin is formed, and, if this is removed, the fluid which remains 

 is plasma minus fibrinogen, and is called serum. 



When serum is treated with an equal volume of a saturated solution 

 of ammonium sulphate, a precipitate of serum globulin is obtained. 

 This precipitate is found to be a mixture of two substances, one of 

 which, euglobulin, is a true globulin, while the other, pseudo-globulin, 

 resembles albumin in being soluble in distilled water. If serum from 

 which serum globulin has been removed is saturated with ammonium 

 sulphate, a further precipitate of serum albumin is obtained. The 

 filtrate from this contains no other protein. Fibrinogen coagulates at 

 about 56 C., serum globulin at 75, and serum albumin at a slightly 

 higher temperature. 



Although albumin and globulin can be separated from serum by 

 chemical methods, there is reason to believe that in the serum itself 

 these two substances are combined to form one serum protein. 



