404 FOOD AND DIGESTION 



Proteins. The usual protein tests (page 107) can be applied to gastric 

 juice and show that it contains small quantities. 



11. Artificial Gastric Juice. The active principle, pepsin, of gastric 

 juice can be obtained by extracting the gastric mucous membrane of the 

 dog, pig, etc. Scrape off the mucous membrane, grind it to a fine pulp by 

 repeatedly running it through a sausage machine or by pounding in a mortar 

 with clean sand. The mucous membrane should be allowed to stand for 

 three or four hours before extraction, otherwise the zymogen, and not the 

 enzyme, will be obtained. Extract a portion of this gastric pulp in water and 

 filter. Or extract with glycerin for several weeks and filter. Either of these 

 extracts contains the enzyme. A solution of the glycerin extract in o . 2 per 

 cent, hydrochloric acid contains all the properties of gastric juice. This 

 solution is known as artificial gastric juice. 



Commercial pepsin already prepared can be obtained on the market. 

 Artificial gastric juice is made from commercial pepsin by adding 0.5 

 grams scale pepsin per hundred cc. of 0.2 per cent, hydrochloric acid, which 

 gives a very active preparation. 



12. Digestive Action of Gastric Juice, or Artificial Gastric Juice 

 on Proteins. The chief digestive action of gastric juice is on proteins. 

 Shreds of fibrin which permit the gastric juice to come in intimate contact 

 with all parts of the material form the best protein for testing the action of 

 this enzyme. Prepare a series of test-tubes, a, b, c, d, each containing 5 cc. 

 of artificial gastric juice. Add to a some shreds of fibrin; to b some boiled 

 white of egg; to c some fibers of boiled meat; to d some fibers of raw 

 meat; place in a warm bath at 40 C. and examine at intervals of 20 

 minutes. Tabulate the results by the plan indicated in Experiment 13, 

 noting particularly the rapidity with which the different proteins go into 

 solution. 



13. Condition Affecting the Enzyme Action of Gastric Juice. Pre- 

 pare a series of test-tubes containing 5 cc. each of gastric juice, according 

 to the table on the next page. Add fibrin threads to each and note the 

 changes at intervals of 10 minutes. 



14. The Effect of Bile on Peptic Digestion. The influence of bile 

 on the activity of pepsin-hydrochloric acid is demonstrated in the following 

 steps: i. Place in a series of test tubes, A, B, C, D, 2 cc. each of 0.5 per 

 cent, pepsin hydrochloric acid solution. 2. Add to A 2 cc. of water; B 2 

 cc. water, o.i cc. bile solution (5 per cent, dried bile); C 1.5 cc. water, 0.5 

 cc. bile solution; D 2 cc. bile solution. 3. Add to each test tube 2 cc. of 

 0.4 per cent, hydrochloric acid and shake thoroughly. Drop in each test 

 tube 4 fibrin threads, and set in water bath at 40 C. Tabulate the results 

 at intervals of 10 minutes. 



15. Cleavage Products of Gastric Digestion. Add 5 to 10 grams 

 of fibrin to 500 cc. of artificial gastric juice in a flask and place in a water- 

 bath at 40 C. After one hour filter off 100 cc. Exactly neutralize this 



