THE CHEMISTRY OF BLOOD PLASMA 159 



11. 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 thro\vn 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 antecedents 

 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 

 an equal volume of saturated ammonium sulphate. A second heavier pre- 

 cipitate of serum- globulin separates out. When this is separated, and crys- 

 tals of ammonium sulphate are added to the filtrate to complete saturation 

 at 40 C., a third precipitate of serum-albumin separates. 



Each of these precipitates may be redissolved and purified by reprecipi- 

 tation and can be tested by the characteristic protein reactions, see page 107, 

 which they all give. 



b. Sugars of Blood Plasma or Serum. If a quantity of blood serum is 

 diluted with about 5 to 10 times its volume of water, and the proteins are 

 removed by slight acidulation with acetic acid and boiling and filtering, the 

 filtrate will contain reducing sugar and the various solids of blood plasma. 

 To a concentrated sample of the filtrate add Fehling's solution and boil. 

 A reddish precipitate indicates the presence of reducing sugar. If this ex- 

 periment is done quantitatively, about from o . i to o . 2 per cent, of sugar will 

 be found. 



c. The Salts of Blood Plasma. The salts of blood plasma are tested 

 best by evaporating some of the blood serum to dryness, and burning the 

 residue to oxidize the organic matter and dissolving the ash in water. Test 

 as follows: To a sample add i per cent, of silver nitrate; a white precipitate 

 soluble in an excess of ammonia, but not soluble in nitric acid, indicates 

 chlorides. 



To a second sample add i per cent, barium chloride. If sulphates are 

 present there will be a white precipitate which settles out quickly. 



Acidify a third sample with nitric acid and add ammonium molybdate 

 and heat. A yellow precipitate indicates the presence of phosphates. 



To the fourth sample add an excess of strong ammonia and i per cent, 

 ammonium oxalate, heat. A white precipitate indicates the presence of 

 calcium. 



12. Blood Corpuscles. The characteristic substance in the composi- 

 tion of the corpuscles is the pigment known as hemoglobin, and this is the 

 only chemical factor that will be considered in these experiments. 



