THERMAL DEATH POINT 201 



of broth in the rack in the water bath and heat slowly until 

 the thermometer in the tube of broth registers 45 C. 



5. Hold at this temperature for fifteen minutes. 



Note. Slow heating is necessary in order that the respective 

 temperatures may be held for the desired period of time. 



6. Without removing the tubes from the bath, inoculate 

 one tube of broth witfy a loopful of the broth culture of 

 B. typhosus, a second with B. mycoides. Carefully mix the 

 inoculum with the broth without removing the tubes. Mark 

 each tube carefully. 



7. Allow these inoculated tubes to remain in the water 

 bath at 45 C. for ten minutes. 



8. Remove and place immediately in cold water. 



9. Incubate each organism at its optimum temperature 

 after each trial. 



10. Next, raise the temperature of the bath five degrees, 

 i.e., to 50 C. and inoculate the tubes as before with B. 

 typhosus and B. mycoides. 



11. Keep the tubes at 50 C. for ten minutes, remove 

 them from the bath, cool and incubate. 



12. In the same manner expose the organism to the 

 following temperatures, 55, 60, 65 and 70, for a period 

 of ten minutes each. 



13. In all cases incubate seven days and record as the 

 thermal death point (t. d. p.) the lowest temperature at 

 which growth fails to appear. 



14. What are the standard methods for the determina- 

 tion of the t. d. p.? What are the flaws in the above 

 method? What different factors may influence the thermal 

 death point of an organism? 



Do all organisms possess the same t. d. p.? Explain. 



15. Give data and results in full. Draw any conclusions 

 that properly follow and point out any practical applica- 

 tions. 



