198 GENERAL MICROBIOLOGY 



Stop transferring when you find that there is no growth 

 in the test tube last inoculated. 



4. What influence has the physical condition of the sub- 

 strate upon which the microorganisms are dried upon their 

 longevity? Illustrate. 



What dried cultures of microorganisms have been used 

 with success commercially? Without success? What other 

 methods may be employed to demonstrate the effect of 

 desiccation on microorganisms? 



5. State all results in full and draw any conclusions. 

 Point out any possible practical applications. 



REFERENCES 



MARSHALL: Microbiology, pp. 151-152, 280-283, 338-343, 367-369, 



374-380, 428-429, 453-460. 



SMITH, E. F.: Bacteria in Relation to Plant Diseases, Vol. I, pp. 70-71. 

 EYRE: Bacteriological Technic, 2d Ed., pp. 306-308. 



EXERCISE 21. THE DETERMINATION OF THE OPTI- 

 MUM, MAXIMUM AND MINIMUM TEMPERATURE 

 REQUIREMENTS FOR CERTAIN ORGANISMS 



Apparatus. Sixteen tubes of dextrose broth. 



Cultures. Sacch. cerevisice; B. subtilis; Oospora lactis; 

 Bad. aerogenes. 



Method. 1. Inoculate four tubes of dextrose broth with 

 each organism. 



2. Place one culture of each organism at each of the 

 following temperatures: 5, 25, 37, and 45. 



3. Note the growth as to vigor after twenty-four, forty- 

 eight, seventy-two hours and seven days. Tabulate the data. 



4. What is the natural habitat of each organism? Does 

 this explain your results in any way? 



What is the biological significance of the cardinal points 

 of temperature? In what industries making use of micro- 

 organisms is the regulation of temperature especially 

 important? 



