PROTEINS 255 



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. 



1. 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. 



(1) With small pieces, test its solubility in water and 10% 

 NaCl. 



(2) 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. Observe that solution takes place. Neutralize 

 each carefully. The precipitate indicates that the protein was 

 converted into metaprotein. 



(3) 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. Note that the coagulated albumin is readily digestible. 



(4) With a small piece of egg white in water try Millon's 

 reaction and the xanthoproteic test. Both are positive. 



(5) Biuret test. Partly dissolve a piece of egg white in concen- 

 trated NaOH. Cautiously add very dilute copper sulphate. Ob- 

 serve 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. 



(a) Proteoses. The intermediary products of protein hydro- 

 lysis are somewhat arbitrarily subdivided into various groups 

 distinguished by the concentration of ammonium sulphate neces- 

 sary to cause their precipitation and by other similar character- 

 istics. Products which are not precipitated by ammonium sul- 

 phate are said to have passed beyond the proteose state. 

 "Witte's peptone" and "Armour's peptone" are in reality mix- 



