25 



of copper sulphate is used. They give a pink instead of 

 a violet color. (Also true of albumoses. ) The pink color 

 is also given by the substance called biuret, hence the test is 

 often called the biuret reaction. (Biuret is formed by heat- 

 ing urea ; ammonia passes off and leaves biuret, thus : 

 aCONjH^ (urea)— NH3 (ammonia) equals C^O^NjHj (biuret). 



108. To the third portion add neutral ammonium .sulphate 

 to saturation. This precipitates all of the albumoses while 

 the peptones remain in solution. Filter and test the filtrate 

 for peptones by the biuret test as follows : Take another test- 

 tube and put a few drops of i % solution of copper sulphate 

 in it ; empty it out so that the merest trace of the copper 

 .sulphate is adherent to the wall of the tube, then add the 

 filtrate and a few drops of strong caustic potash. A pink 

 color (biuret reaction) should be produced. 



109. If digestion has been quite complete the tests for 

 acid-albumin and albumose may not be very satisfactory. 

 The main fact, however, that an indiffusible proteid, before 

 being converted into a diffu.sible peptone, must pa.ss through 

 intermediate forms — acid-albumin and albumose — is import- 

 ant, and must be kept in mind in this aud succeeding ex- 

 periments. 



1 10. After filtering, treat the contents of the tubes con- 

 taining meat, bread, potato, albumin, butter and mixed sub- 

 stances according to the above tests. 



X. 



III. Pancreatic Digestion. The pancreas of the pig, ox, 

 or dog is perhaps the be.st adapted for class experimentation. 

 Their various ferments are active and usually give clear and 

 definite results. The steaptic or fat-splitting ferment is 

 generally the most difficult one of the four to demonstrate, — 

 the fresh pancreas being necessary for this purpose. The 



