GASTRIC DIGESTION. 141 



1. Take a sample and boil it. There should be no coagulable 



proteid. 



2. Neutralise another portion carefully using litmus as an 



indicator. There will be a pp of acid proteid. 



Add some warmed dilute HC1 to the digestion to fill the 

 beaker, arid test samples, as follows, from time to time. 



As soon as test (2) gives markedly diminished results and 

 the tests (3) and (4) are well marked, set two-thirds of a beaker- 

 ful aside, neutralise and label it (A). 



To the remainder add one volume warm dilute HC1, and 

 continue the digestion. 



3. HNO 3 a few drops. A white pp which disappears on heating 



and returns on cooling (proto-proteose). 



4. Two drops of acetic acid and a few of ferrocyanide of 



potassium solution. A white pp which disappears with 

 heat and returns on cooling (proto- and deutero-proteose). 



5. Add one-quarter volume NaOH and one or two drops of 



CuSO 4 solution. Biuret reaction. Pink indicates proteoses 

 as well as pepton. 



When test 5 is the only reaction given, then nothing but 

 pepton is present. This stage will, however, not be reached 

 during the time which is at the disposal of the class. 



6. Saturate some of the fluid with Am 2 SO 4 whilst boiling and 



first acidify by means of a little acetic acid, then 

 neutralise with NaOH solution, boiling after each addition ; 

 filter and test the filtrate for pepton, by adding four 

 volumes of NaOH solution and then a few drops of CuSO 4 . 

 Boiling in different reactions has the effect of precipi- 

 tating the proteoses completely. The excess of alkali 

 in the Biuret test is to set aside the effect of the 

 Am 2 SO 4 which would interfere with the reaction. 



