64 FERMENTATION. 



153. Separate the mucous membrane from the muscular 

 coating of a pig's stomach; chop finely and allow to stand several 

 hours with two or three times its weight of dilute phosphoric acid 

 (1 per cent.). Filter and to the filtrate, which contains the pepsin, 

 add lime-water until the reaction is alkaline. The calcium phos- 

 phate which falls carries down the pepsin with it. Filter and dis- 

 solve the precipitate in dilute HC1. Place in a dialyzer, changing 

 the water outside frequently. The acids and salts diffuse out, 

 leaving the pepsin inside the dialyzer, as can be proved by adding 

 it to 0.2-per-cent. HC1 and seeing that it will digest fibrin. 



154. Test a part of the precipitated pepsin which has been 

 obtained with the calcium phosphate for nitrogen. This may be 

 done, after washing with water, by drying the precipitate, still 

 mixed with calcium phosphate, then mixing with twice as much 

 soda-lime and testing in a dry tube. The nitrogen is converted 

 into ammonia, which may be recognized by the odor and by its 

 action on red litmus-paper. 



155. To a part of the dialyzed-pepsin solution obtained in 

 Experiment 153 add finely powdered ammonium sulphate, stirring 

 meanwhile as long as it dissolves. The pepsin is precipitated like 

 the albuminous compounds. Filter, dissolve the precipitate in a 

 0.2-per-cent. HC1 solution, and show that it will digest fibrin. 



156. Collect some saliva in a test-tube, place the 

 latter in a beaker of water, and raise the temperature of 

 the water to 65 or 70 C. Keep it at this point for five 

 minutes. Then let a little of it stand a few minutes with 

 a starch solution, testing afterward with Trommer's test. 

 N~o glucose is produced, the ferment, ptyalin, having been 

 destroyed by the heat. 



157. Collect a considerable quantity of saliva, and 

 put it into two tubes. Quickly cool one nearly to freezing 

 and warm the other to body-temperature. Add to these 

 an equal amount of starch solution. Allow the action to 

 proceed for five minutes, then raise them both to the boil- 

 ing-point to stop fermentation. Determine the amount of 



