A Practical Physiology: A Text-Book for Higher Schools · Chapter 10Additional Experiments
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Experiment 66. Test a portion of C (Experiment 57) with solution of iodine; no blue color is obtained, as all the starch has disappeared, having been converted into a reducing sugar, or maltose.
Experiment 67. Make a thick starch paste; place some in test tubes, labeled A and B. Keep A for comparison, and to B add saliva, and expose both to about 104° F. A is unaffected, while B soon becomes fluid—within two minutes—and loses its opalescence; this liquefaction is a process quite antecedent to the saccharifying process which follows.
Experiment 68. To show the action of gastric juice on milk. Mix two teaspoonfuls of fresh milk in a test tube with a few drops of neutral artificial gastric juice;[30] keep at about 100° F. In a short time the milk curdles, so that the tube can be inverted without the curd falling out. By and by whey is squeezed out of the clot. The curdling of milk by the rennet ferment present in the gastric juice, is quite different from that produced by the “souring of milk,” or by the precipitation of caseinogen by acids. Here the casein (carrying with it most of the fats) is precipitated in a neutral fluid.
Experiment 69. To the test tube in the preceding experiment, add two teaspoonfuls of dilute hydrochloric acid, and keep at 100° F. for two hours. The pepsin in the presence of the acid digests the casein, gradually dissolving it, forming a straw-colored fluid containing peptones. The peptonized milk has a peculiar odor and bitter taste.
Experiment 70. To show the action of rennet on milk. Place milk in a test tube, add a drop or two of commercial rennet, and place the tube in a water-bath at about 100° F. The milk becomes solid in a few minutes, forming a curd, and by and by the curd of casein contracts, and presses out a fluid,—the whey.
Experiment 71. Repeat the experiment, but previously boil the rennet. No such result is obtained as in the preceding experiment, because the rennet ferment is destroyed by heat.
Experiment 72. To show the effect of the pancreatic ferment (trypsin) upon albuminous matter. Half fill three test tubes, A, B, C, with one-per-cent solution of sodium carbonate, and add 5 drops of liquor pancreaticus, or a few grains of Fairchild’s extract of pancreas, in each. Boil B, and make C acid with dilute hydrochloric acid. Place in each tube an equal amount of well-washed fibrin, plug the tubes with absorbent cotton, and place all in a water-bath at about 100° F.
Experiment 73. Examine from time to time the three test tubes in the preceding experiment. At the end of one, two, or three hours, there is no change in B and C, while in A the fibrin is gradually being eroded, and finally disappears; but it does not swell up, and the solution at the same time becomes slightly turbid. After three hours, still no change is observable in B and C.
Experiment 74. Filter A, and carefully neutralize the filtrate with very dilute hydrochloric or acetic acid, equal to a precipitate of alkali-albumen. Filter off the precipitate, and on testing the filtrate, peptones are found. The intermediate bodies, the albumoses, are not nearly so readily obtained from pancreatic as from gastric digests.
Experiment 75. Filter B and C, and carefully neutralize the filtrates. They give no precipitate. No peptones are found.
Experiment 76. To show the action of pancreatic juice upon the albuminous ingredients (casein) of milk. Into a four-ounce bottle put two tablespoonfuls of cold water; add one grain of Fairchild’s extract of pancreas, and as much baking soda as can be taken up on the point of a penknife. Shake well, and add four tablespoonfuls of cold, fresh milk. Shake again. Now set the bottle into a basin of hot water (as hot as one can bear the hand in), and let it stand for about forty-five minutes. While the milk is digesting, take a small quantity of milk in a goblet, and stir in ten drops or more of vinegar. A thick curd of casein will be seen. Upon applying the same test to the digested milk, no curd will be made. This is because the pancreatic ferment (trypsin) has digested the casein into “peptone,” which does not curdle. This digested milk is therefore called “peptonized milk.”
Experiment 77. To show the action of bile. Obtain from the butcher some ox bile. Note its bitter taste, peculiar odor, and greenish color. It is alkaline or neutral to litmus paper. Pour it from one vessel to another, and note that strings of mucin (from the lining membrane of the gall bladder) connect one vessel with the other. It is best to precipitate the mucin by acetic acid before making experiments; and to dilute the clear liquid with a little distilled water.
Experiment 78. Test for bile pigments. Place a few drops of bile on a white porcelain slab. With a glass rod place a drop or two of strong nitric acid containing nitrous acid near the drop of bile; bring the acid and bile into contact. Notice the succession of colors, beginning with green and passing into blue, red, and yellow.
Experiment 79. To show the action of bile on fats. Mix three teaspoonfuls of bile with one-half a teaspoonful of almond oil, to which some oleic acid is added. Shake well, and keep the tube in a water-bath at about 100° F. A very good emulsion is obtained.
Experiment 80. To show that bile favors filtration and the absorption of fats. Place two small funnels of exactly the same size in a filter stand, and under each a beaker. Into each funnel put a filter paper; moisten the one with water (A) and the other with bile (B). Pour into each an equal volume of almond oil; cover with a slip of glass to prevent evaporation. Set aside for twelve hours, and note that the oil passes through B, but scarcely any through A. The oil filters much more readily through the one moistened with bile, than through the one moistened with water.
Experiment 81. Use olive oil or lard. Show by experiment that they are soluble in ether, chloroform and hot water, but insoluble in water alone.
Experiment 82. Dissolve a few drops of oil or fat in a teaspoonful of ether. Let a drop of the solution fall on a piece of tissue or rice paper. Note the greasy stain, which does not disappear with the heat.
Experiment 83. Pour a little cod-liver oil into a test tube; add a few drops of a dilute solution of sodium carbonate. The whole mass becomes white, making an emulsion.
Experiment 84. Shake up olive oil with a solution of albumen in a test tube. Note that an emulsion is formed.