The Digestion of Food 135 



ADDITIONAL EXPERIMENTS 



Experiment 54. Test a portion of C (Experiment 42) with solution 

 of iodine ; no blue color is obtained, as all the starch has disappeared, 

 having been converted into sugar, or maltose. 



Experiment 55. 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 j 1 keep at about 100 Fahr. 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 56. To the test tube in the preceding experiment add 

 two teaspoonfuls of dilute hydrochloric acid, and keep at 100 Fahr. 

 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 57. 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 Fahr. 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 58. 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. 



1 An artificial gastric juice may be obtained for experimental purposes 

 by dissolving about ten grains of pepsin powder (made by some reputable 

 manufacturer and obtained of any druggist) in half a pint of water and 

 adding perhaps fifteen to twenty drops of strong hydrochloric acid, or 

 about two teaspoonfuls of the dilute acid. 



