ACTION OF ENZYMES UPON STARCH 189 



5. Is there any relation between the power of enzymes 

 to liquefy gelatin and their ability to dissolve casein? What 

 type of proteolytic enzyme dissolves casein? 



6. Give your results in detail. Draw any conclusions 

 which follow and point out any practical applications that 

 may be made. 



REFERENCES 



MARSHALL, C. E. : Microbiology, pp. 138-139, 354. 



HASTINGS : The action of various classes of bacteria on casein as shown 



by milk agar plates. Cent. f. Bakt., II Abt., Bd. 12 (1904) 



p. 590, 



EXERCISE 14. TO SHOW THE ACTION OF ENZYMES 

 UPON STARCH 



Apparatus. Three sterile Petri dishes; three test tubes; 

 soluble starch; three tubes sterile agar; Lugol's iodin solu- 

 tion. 



Cultures. Soil for inoculation. 



Method. 1. Place 0.1 gm. of soluble starch in each 

 test tube, plug and sterilize in the hot air sterilizer. 



2. To each tube of starch add one tube of melted agar. 



3. When at the correct temperature (40-45 C.) inoculate 

 one tube with one loopful of soil. (State type used.) 

 Inoculate the second from the first, etc., then plate all three 

 dilutions. 



4. When the colonies are well developed, pour iodin solu- 

 tion on the plate and note any clearing around the colonies. 

 What does this indicate? 



5. Examine microscopically different types of colonies 

 attacking starch. Are they molds, yeasts, or bacteria? 

 Which type predominates on your plates? 



6. What enzymes are concerned? Give specific action. 

 How is pure enzymic action demonstrated? 



7. Write the theoretical chemical equation. What is 

 soluble starch? 



