DIGESTION OF NITROGENOUS SUBSTANCES. 39 



stituents of milk) into a test-tube, add water, 

 and shake well. 



1. Does the substance dissolve? How do you 



know? 



2. Add a little diluted hydrochloric acid and 



shake. What change do you observe? 



3. Evaporate to dryness in an evaporating- 



dish some of the liquid obtained in 2. 



a. What is the appearance of the sub- 



stance which is left? 



b. Will it dissolve in water? 



c. Into what kind of a salt has hydro- 



chloric acid changed the insoluble 

 salt? 



4. (Hydrochloric acid is one of the ingredients 



of gastric juice.) In what part of the 

 alimentary canal are insoluble salts di- 

 gested, and how are they digested? 



21. DIGESTION OF NITROGENOUS 

 SUBSTANCES. (Dem.) 



Materials : Hard-boiled egg, pepsin, pancreatin, hydrochloric acid, 

 baking-soda; test-tubes, labels. 



A. Action of gastric juice. 

 T. Experiments. 



a. Thoroughly mince a piece of hard- 

 boiled egg and place a portion of 

 it in a test-tube; half nil the tube 

 with water. Label Test No. i, 

 minced egg + water. 



