SPECIAL REACTIONS OF THE ALBUMINS. 37 



ferments. This supposition is materially strengthened by the 

 interesting observations of Schwarzschild that pure trypsin is 

 capable of altering the base of Curtius in such manner that this 

 no longer gives the biuret reaction, while it is incapable of splitting off 

 ammonia from acid amides, such as acetamide, asparagin, and others. 



2. The Xanthoproteic Reaction. A few c.c. of the solution to be 

 tested are treated with concentrated nitric acid, when in the presence 

 of albumin a yellow color develops either at once or upon heating. 

 With some albumins a white flaky precipitate develops at the same 

 time, while with others the solution remains clear. Upon the subse- 

 quent addition of an excess of ammonia the color turns orange, or 

 with caustic soda, a reddish brown. 



The reaction depends upon the formation of certain nitro deriva- 

 tives, and is referable to the presence in the albuminous molecule 

 of a tyrosin group or of an indol complex. It is accordingly not 

 characteristic of albumins alone, and can be obtained with many 

 other substances. 



3. Millon's Reaction. The reagent is a solution of mercuric 

 nitrate containing a little nitrous acid. It is prepared by dissolving 

 a few grammes of mercuric nitrate in an amount of water which is 

 just sufficient for its solution. Any basic salt that may be present is 

 dissolved with fuming nitric acid, when a solution of sodium acetate 

 is added, drop by drop, until the reagent gives a red color on boil- 

 ing with a few drops of a dilute solution of phenol. 



The test is conducted by adding a few drops of the solution to be 

 examined to a few c.c. of the reagent, when in the presence of 

 albumins a white precipitate forms, which turns a brick red on 

 boiling. If the substance to be examined is a solid, this is sus- 

 pended in a few drops of water and treated in the same manner. 



Millon's reaction is common to all benzol derivatives, in which 

 one hydrogen atom has been replaced by a hydroxyl group ; it is 

 consequently obtained with all albumins which on tryptic digestion 

 yield tyrosin. This radicle is absent in glutin and in those albumoses 

 which contain the hemi- group (see later), and these bodies accord- 

 ingly do not give the reaction. 



4. The Reaction of Adamkiewicz. A particle of the dry albumin- 

 ous substance which should contain as little fat as possible is dis- 

 solved in about 6 c.c. of glyoxylic acid by the aid of heat, and 

 underlayed with an equal volume of concentrated sulphuric acid. 

 Immediately or on boiling red, green, and violet rings form at the 

 zone of contact with the sulphuric acid, and on shaking the entire 

 fluid turns violet. At the same time it becomes slightly fluorescent, 

 and on spectroscopic examination gives a broad band extending from 

 yellow to blue. Albuminous solutions are similarly treated. 



The reaction is referable to the tryptophan complex, viz., to 

 skatol-amino-acetic acid (Hopkins and Cole). 



Neubauer and Rohde suggest the following reaction as a test for 

 the tryptophan complex : An aqueous solution or suspension of 



