78 THE GASTRIC JUICE. 



several days without danger of putrefaction provided it 

 contains 0.2 per cent, of the free acid. 



When the fibrin has nearly or quite disappeared boil 

 one-half the liquid to coagulate any unchanged albumin- 

 ous compound, and filter. The filtrate contains the prod- 

 ucts of digestion: acid albumin, albumoses, and peptones. 

 The proportion of each varies with the time of digestion. 

 The amount of peptones is usually small until the pepsin 

 has acted for a considerable time. 



185. Precipitate the acid albumin by neutralizing 

 carefully with very dilute sodium hydrate. Filter it out 

 and test as in Experiments 104 and 105. 



186. From the filtrate precipitate the albumoses by 

 saturating the solution with ammonium sulphate by the 

 aid of heat. Filter and test the precipitated albumoses as 

 in Experiments 116 and 117. 



187. The filtrate from the albumoses contains the 

 peptones. Test it according to the tests used in Experi- 

 ments 119, 121, and 122. When the biuret test is made 

 in presence of ammonium salts a large excess of sodium 

 hydrate must be used. Allow the second half of the diges- 

 tion to proceed for a week before testing for peptones, add- 

 ing hydrochloric acid if it is exhausted. 



188. PREPARATION OF RENNIN. Extract the chopped mu- 

 cous membrane with 0.2-per-cent. hydrochloric acid, as in Experi- 

 ment 179. Both rennin and pepsin go into solution. Stir the 

 membrane well in the acidified water, but do not let it stand a 

 very long time, as the rennin is digested in an acid solution by the 

 pepsin. Neutralize carefully, add a small amount 'of magnesium 

 carbonate, and shake well. The pepsin adheres to the carbonate 

 and can be filtered out with it. Shake the filtrate with another 

 portion of magnesium carbonate, filter, and repeat the operation 

 until the pepsin is removed, which can be shown by the failure of 

 an acidified portion of the filtrate to dissolve fibrin. The filtrate 

 containing the rennin should coagulate milk in a few minutes. 



