206 GENERAL MICROBIOLOGY 



range differ with different organisms? Explain the action 

 occurring. 



6. In each case inoculate heavily the first tube at either 

 or both extremes, in which the organism fails to grow, 

 from the tube just next it in series which shows growth. 

 Does this freshly inoculated tube show signs of growth after 

 twenty-four to forty-eight hours? Explain the action which 

 occurs. 



7. Which organisms are acidophiles? 



What is the optimum, the minimum and the maximum 

 reaction for each organism according to this experiment? 



What factors not considered in this experiment might 

 influence results? 



How would you determine the exact optimum reaction 

 of an organism? 



8. Give all data and results in full and draw conclusions. 

 Point out any practical applications. 



REFERENCES 



MARSHALL: Microbiology, pp. 173-180, 235-237. 

 EYRE: Bacteriological Technic, 2d Ed., pp. 305-306. 



EXERCISE 27. TO DETERMINE THE INFLUENCE OF 

 DIFFUSED LIGHT ON MOLDS 



Apparatus. Sterile deep culture dish; tube of dextrose 

 agar or gelatin; black paper. 

 Culture. Rhizopus nigricans. 

 Method. 1. Pour a tube of agar into a deep culture dish. 



2. When solid, inoculate with Rhizopus nigricans. 



3. Wrap the dish closely in black paper so that no light 

 can penetrate. 



4. Cut a hole 2 to 3 cm. in diameter in the top edge of 

 the paper and place the dish in a north window so that 

 only diffused light will enter the aperture. 



5. Allow the dish to stand ten days, then examine it. 

 How does diffused light influence this mold? 



