1 64 THE BLOOD 



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 salts 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 0.2 percent, of sugar will 

 be found. The sugar may be separated from the serum by dialysis through 

 collodian membranes. 



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 blood corpuscles is the pigment known as hemoglobin, and this is 

 the only chemical factor that will be considered in these experiments. 



a. Hemoglobin Crystals. Take a sample of dog's blood, or if a centri- 

 fuge is available separate and wash a sample of blood corpuscles, and 

 mix with about three volumes of saturated ether water, or if blood is used 

 dilute with two or three volumes of water and add about 10 per cent, by 

 volume of pure ether and shake thoroughly. Crystals of oxyhemoglobin 

 will be formed, and these can be mounted and examined with a microscope. 



b. Spectrum of Hemoglobin and its Compounds. 



i. Oxyhemoglobin. Dilute a sample of defibrinated blood with about 

 ten volumes of distilled water. From this stock solution make five solutions 

 all differing by 33^ per cent. Examine these with a direct-vision spectro- 

 scope. Make a drawing showing the absorption spectrum of each sample 



