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_.