608 APPENDIX 



liquid. It carries in solution all substances absorbed from the diges- 

 tive tract; all waste products of cell activity; all hormones; and 

 all of the great group of unidentified materials that are concerned 

 with the control of infection. The most prominent constituents 

 of blood belong in the chemical group of proteins. 



Tests for Blood Proteins. The Xanthoproteic Reaction. Pour in a 

 test tube concentrated blood serum to the depth of J4 inch. Add 

 3 or 4 drops of concentrated nitric acid (HNO 3 ). (Handle with 

 care.) Boil and cool. A yellow precipitate is formed and the solu- 

 tion becomes yellow. Add strong sodium hydrate (NaOH). 

 (Handle with care.) When sufficient has been added the color 

 becomes much deeper. 



The Biuret Reaction. Pour a little blood serum into a test tube. 

 Add a few drops of very dilute copper sulphate (CuS0 4 ). Make 

 alkaline with sodium hydrate (NaOH). A rose color is produced. 

 These two tests are characteristic for proteins. 



Iron in Hemoglobin. The essential substance of red corpuscles 

 is an iron-containing pigment compound, hemoglobin. The prop- 

 erty of hemoglobin as an oxygen-carrier depends on its iron 

 content. 



A Chemical Test for Iron. Place a few iron filings in a test tube. 

 Pour into the test tube, under the hood, a few drops of aqua regia 

 (nitric and hydrochloric acids). The fumes of aqua regia are very 

 irritating and the fluid is very corrosive. Handle with great care, 

 always under the hood, and avoid inhaling the fumes. After al- 

 lowing a few minutes for some iron to be dissolved, dilute with an 

 inch of water and add a few drops of potassium ferrocyanide solu- 

 tion. A characteristic deep blue precipitate of iron ferrocyanide 

 (prussian blue) is the test for iron. 



To demonstrate the presence of iron in blood, place a few lumps 

 of dried blood in a porcelain crucible over a bunsen flame under a 

 hood. Continue heating the mass, stirring occasionally with a 

 glass rod, until only a reddish ash is left. Allow the crucible to 

 cool. Add a few drops of aqua regia. Warm gently. After the 

 solution has cooled again dilute with water, pour into a test tube 

 and add potassium ferrocyanide solution. The appearance of 

 abundant prussian blue shows the presence of iron in the ash of 

 blood. 





