200 GENEKAL MICROBIOLOGY 



8. Compare the three sets of cultures and note the 

 variations from the normal type of growth. Tabulate your 

 data. 



9. Are all of these organisms pecilothermic? What 

 are termed the cardinal points of temperature for micro- 

 organisms? What is the lowest temperature at which 

 growth, even of the feeblest kind, is possible? What term 

 is applied to organisms which grow best at low tempera- 

 tures? 



10. Give all results and answers in full and draw any 

 conclusions permissible. Point out the practical applica- 

 tions that may be made. 



REFERENCES 



FISCHER: Structure and Functions of Bacteria, pp. 73-75. 

 MARSHALL: Microbiology, pp. 154-155, 158-159, 199, 318, 395-401. 

 LAFAR: Technical Mycology, Vol. I, pp. 58-60. 



EXERCISE 23. THE DETERMINATION OF THE THER- 

 MAL DEATH POINT OF A SPORE-FORMING AND A 

 NON-SPORE-FORMING ORGANISM 



Apparatus. Water bath; test-tube rack to fit bath; 

 ring tripod; Bunsen burner; thermometer; thirteen test 

 tubes of uniform diameter containing exactly 10 c.c. of 

 broth; platinum loop 4 mm. in diameter; dish containing 

 cold water (20 G. or below). 



Cultures. Twenty-four to thirty-six hour broth cultures 

 of B. typhosus and B. mycoides. 



Method. 1. Examine the cultures for the presence or 

 absence of spores. 



2. Set up the water bath on the ring tripod, place only 

 sufficient water in it to cover the medium in the test tubes 

 and insert the test-tube rack. 



3. Insert the thermometer into one of the test tubes 

 of broth, passing it through the cotton plug. 



4. After flaming the plugs, place all the remaining tubes 



