104 PHYSIOLOGY 



(3) MILLON'S REACTION. Millon's reagent is a solution of 

 mercuric nitrate in water containing free nitrous acid. On adding a 

 few drops of this to a protein solution a white precipitate is produced 

 which turns a brick-red colour on boiling. It depends on the presence 

 in the protein of a hydroxy- derivative of benzene, and is determined 

 in the protein by the tyrosine, which is oxyphenylalanine. 



(4) SULPHUR REACTION. On warming a solution of protein 

 with caustic soda in the presence of lead acetate a black colour is 

 produced owing to the precipitation of lead sulphide. The depth of 

 coloration gives a rough indication of the amount of sulphur in the 

 protein under investigation. 



(5) THE HOPKINS-ADAMKIEWICZ REACTION. It was stated 

 by Adamkiewicz that on the addition of acetic acid and concentrated 

 sulphuric acid to protein, a violet colour was produced. Hopkins 

 and Cole showed that the success of this reaction depended on the 

 presence of glyoxylic acid CHO.COOH as an impurity in the acetic 

 acid used. The test is therefore performed now as follows : 



Glyoxylic acid is prepared by the action of sodium amalgam 

 on a solution of oxalic acid. A few drops of this solution are added to 

 the solution of protein, and strong sulphuric acid poured down the 

 side of the tube. A bluish-violet colour is produced at the junction 

 of the two fluids. This reaction is due to the presence in the protein 

 of tryptophane. 



The so-called Liebermann's reaction has been shown by Cole to be essen- 

 tially a modification of the above, and is due also to the presence of tryptophane. 

 In this test the protein is precipitated by alcohol, washed with ether, and heated 

 with concentrated hydrochloric acid, when a blue colour is produced, glyoxylic 

 acid being derived from the alcohol and ether. 



(6) REACTIONS INDICATING THE PRESENCE OF CARBO- 

 HYDRATES. Molisch's test is applied as follows. A few drops of 

 alcoholic solution of a-naphthol and then strong sulphuric acid are 

 added to a protein solution. A violet colour is produced, which on 

 addition of alcohol, ether, or potash turns yellow. The reaction is 

 determined by the presence, either as an impurity or a constituent 

 part of the molecule, of a carbohydrate radical which, under the 

 influence of strong sulphuric acid, is converted into furfurol. The 

 furfurol gives the colour reaction with the a-naphthol. 



Another test for the carbohydrate radical is the orcin reaction. 

 A small quantity of the dried albumin is added to 5 c.c. of fuming 

 hydrochloric acid, and the mixture is then warmed. When the 

 albumin is nearly all dissolved a little solid orcin is added on the point 

 of a knife, and then a drop of ferric chloride solution. After warming 

 this mixture for some minutes a green colour is produced which is 

 soluble in amyl alcohol and gives a definite absorption spectrum. 



