PROTEINS 291 



pared in the same manner as acid metaproteins, using 0.4% 

 sodium hydroxide in place of the acid. Its properties are similar 

 to those of acid metaprotein, with the exception that it gives a 

 less definite neutral sulphur test, as a portion of the sulphur is 

 split off in its manufacture. 



Coagulated Proteins. These protein derivatives are pro- 

 duced from proteins by the action of heat, by standing under 

 alcohol, by the action of certain enzymes, and in various other 

 ways. Much of the protein material of our food is coagulated 

 by cooking before ingestion. 



71. Measure about 10 c.c. of undiluted egg white into a thin- 

 walled test tube and immerse the tube in boiling water for 6-8 

 minutes. Observe the progress of coagulation. Remove the coag- 

 ulated protein from the tube by means of a glass rod, or the wire 

 handle of a test tube brush. 



With small pieces, test its solubility in water and 10% NaCl. 



72. In each of two test tubes put small pieces of the egg white. 

 To one add 0.5% NaOH, to the other 0.2% HC1. Warm to 40 

 for some time. What happens ? Neutralize each carefully. The 

 precipitate indicates that the protein was converted into meta- 

 protein. 



73. Place pieces of egg white in each of two test tubes and 

 test their digestibility by pepsin and trypsin, adding a drop of 

 chloroform and a little toluol and digesting several hours in the 

 incubator. 



74. With a small piece of egg white in water try Millon's 

 reaction and the xanthoproteic test. 



75. Biuret test. Partly dissolve a piece of egg white in con- 

 centrated NaOH. Cautiously add very dilute copper sulphate. 

 Observe the lavender biuret color. From the above results it ap- 

 pears that coagulated albumin still belongs to the protein group. 

 The exact nature of the alterations in the protein molecule 

 brought about by coagulation is not understood. 



2. Secondary Protein Derivatives. 



Proteoses. The intermediary products of protein hydrol- 

 ysis are somewhat arbitrarily subdivided into various groups 



