DIGESTION AND ABSORPTION. 165 



On which of the proteid solutions would one get 



a precipitate with silver nitrate independent of the 



presence of proteid? 



(7) To separate peptone from other proteids. It will have 

 been noted that ammonium sulphate precipitates all 

 proteids except pure peptone. If one has peptone 

 mixed with proteoses and unchanged proteids one may 

 demonstrate its presence by precipitating out the other 

 proteids and then demonstrating by such a test as the 

 Biuret test the presence of a proteid in the clear fil- 

 trate; that could be nothing else than peptone. 



Test commercial peptone in this way and determine 

 whether any appreciable proportion of it is peptone. 

 () The diffusibility of proteids. Fill seven dialyzers 

 with the proteids above studied. 



On the following day test the diffusates for proteids. 



