188 GENERAL MICROBIOLOGY 



prove that xylol has this action? What other chemicals 

 could be used in place of xylol? 



11. What is the object of adding phenol to the gelatin? 

 Would 5% phenol serve the same purpose? Give reason 

 for answer. What other chemicals could be used in place of 

 phenol? Why? What chemicals could not be used in 

 place of phenol? Why? How else may pure enzyme action 

 be demonstrated? 



12. Add 5 drops of 40% formaldehyde (formalin) to 

 each tube of the duplicate liquefied gelatin cultures and 

 note whether they become solid again in a. few days. Ex- 

 plain the action. 



13. Give your results in full and draw any conclusions 

 possible. What practical applications of the above may be 

 made? 



REFERENCES 



BAYLISS: Nature of Enzymic Action, p. 37. 



MARSHALL, C. E.: Microbiology (1911), pp. 134, 138, 141. 



EULER, HANS: General Chemistry of the Enzymes (1912), pp. 115-123. 



VERNON, H. M.: Intracellular Enzymes (1909), pp. 215-220. 



EXERCISE 13. TO SHOW THE ACTION OF PRO- 

 TEOLYTIC ENZYMES UPON CASEIN 



Apparatus. Five tubes of sterile milk; two tubes 

 nutrient agar; sterile 5 c.c. pipettes; two sterile Petri dishes. 



Cultures. Bad. lactis acidi; B. ramosus; B. coli; 

 B. violaceus. 



Method. 1. Warm the milk (40-45 C.). 



2. Place 2 c.c. in each sterile Petri dish and pour one tube 

 of melted agar upon it, mix thoroughly by carefully tilting. 



3. When solid, make parallel streaks with Bact. lactis 

 acidi and B. ramosus upon one and of B. coli and B. viola- 

 ceus upon the other. Transfer cultures -to litmus milk also. 



4. Examine streak cultures every day for evidences of 

 proteolysis. Make drawings and compare the rate of action 

 of the different bacteria. Compare streak with milk cultures. 



