1. Materials

An egg, fibrin, bread, milk, pepsin, hydrochloric acid.

2. Preparation. - Artificial Gastric Juice

Prepare a liter or a quart of 0.2-per-cent hydrochloric acid. To half of this add as much pepsin as will lie upon a small penknife blade. While this is not a standard artificial gastric juice, it is well adapted to our simple experiments.

3. Experiments And Observations

(1) To a bit of starch paste of the consistency of jelly add artificial gastric juice; keep warm; note results, if any, one hour later.

(2) To a few drops of olive oil or a bit of fat add a few cubic centimeters of gastric juice; keep warm; note results.

(3) To a bit of fibrin in a test-tube add gastric juice; keep the mixture warm; note the changes which take place during the next five minutes.

4. To Determine The Active Factors Of Gastric Digestion

(a) To a few shreds of fibrin in a test-tube add a few cubic centimeters of 0.2-per-cent hydrochloric acid. Carefully note results. Will dilute hydrochloric acid dissolve fibrin? Is it possible to digest a proteid without dissolving it ? (b) To fibrin add a neutral aqueous solution of pepsin. Is solution affected? (c) To tube (a) add a few drops of a solution of pepsin, (d) To tube (b) add two volumes of 0.2-per-cent hydrochloric acid. Note results. Formulate conclusions.

5. The Influence Of Division Upon The Time Required To Digest Proteids

Boil an egg ten minutes; cool quickly; separate hard, Coagulated white from yolk and envelopes.

(a) Cut out a one-centimeter cube and put it into a beaker with 40 c.c. artificial gastric juice.

(b) Prepare another beaker in which are sixteen quarter-centimeter cubes in 10 c.c. of artificial gastric juice.

(c) Into another beaker with 10 c.c. of artificial gastric juice put one quarter of a cubic centimeter of the egg albumin, which has been finely divided by pressing through a fine sieve or grinding in a mortar.

Note time required in each case to completely digest albumin.

Has this any hygienic bearing?

6. Steps Of Gastric Digestion

(a) Pass coagulated egg-white through a fine sieve; put half teaspoonful of the divided egg albumin in fifty cubic centimeters of artificial gastric juice. Test the liquid every five minutes for an hour with a view to determining the presence in the liquid of acid albumin, of the proteoses, and of peptone. In what order and after what length of time do the several products appear?

7. Digestion Of Various Proteins

In a series of test-tubes watch the digestion of gelatin, the gluten of bread, the casein of milk, and the myosin of finely shredded fresh meat.

To demonstrate the presence of peptone in these various experiments use the biuret test described in Chapter I (The Needs Of The Body. A. The Chemical Composition Of The Body) of this Appendix.