39 



down the albumoses or proteoses in the form of a white pre- 

 cipitate. Albumose like peptone is soluble in water, and gives 

 the biuret reaction. Ammonium sulphate precipitates all of 

 the proteids but peptone. 



Another test for albumose is to add sodium chloride and a few drops of 

 nitric acid. A precipitate should appear which is dissolved on heating, but re- 

 appears on cooling, indicating the presence of albumose. 



126. Peptones behave differently from the native pro- 

 teids in the copper sulphate and caustic potash test, if only a 

 trace 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 heating 

 urea ; ammonia passes off and leaves biuret, thus : 2CON2HJ 

 (urea) — NH, (ammonia) equals CjO^N^H^ (biuret). 



127. To the third portion add neutral ammonium sul- 

 phate to saturation. This precipitates all of the albumoses 

 and proteids 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 1% 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. 



128. If digestion has been quite long and complete the 

 tests for acid-albumin and albumose may not be very satisfac- 

 tory as these substances may have been converted into pep- 

 tones. They are more readily found shortly after digestion 

 has begun. The main fact, however, that an indiffusible 

 proteid, before being converted into a diffusible peptone, must 

 pass through intermediate forms— acid albumin and album- 

 ose — is important, and must be kept in min^ in this and 

 succeeding experiments. 



129. After filtering, treat the contents of the tubes con- 

 taining meat, bread, potato, albumin, butter, milk, gelatin, 

 and mixed substances according to the above tests. 



130. Drugs on gastric digestion. Use the same prepar- 

 ations as in 113. Put in each test tube 4 cc. 0.2% hydrochloric 

 acid, 2 cc. gastric extract and 4 cc. of the given drug. Keep 

 the tubes at 40° C. for a number of hours or over night and 

 test for peptones. 



