CHAPTER XXI 



DETERMINATIONS OF THERMAL DEATH-TIME 



J. RUSSELL ESTY 

 Research Laboratories, National Canners Association, San Francisco 



Studies on thermal death-points date back to 1745, when Needham showed that 

 boiling an infusion of mutton gravy and soup from seeds to kill all living things and 

 sealing it hermetically did not prevent "spontaneous generation" since some flasks 

 became cloudy. About 1760 Spallanzani, believing that Needham had not heated the 

 bottles long enough or plugged them tightly enough, and after heating an extensive 

 series of flasks containing an infusion of peas and almonds, recommended boiling for 

 three-quarters of an hour. In 1861 Pasteur demonstrated that heating at 110° C. 

 (230° F.) under pressure may be necessary to prevent "spontaneous germination." 

 In 1870 Ferdinand Cohn showed that irregular results following heating were due to 

 the survival of spores which, according to later workers, were able to resist varying 

 degrees of heat. 



DESTRUCTION OF SPORES 



Bredfeld' reported that spores of B. subtUis required 3 hours at 100° C. 

 (212° F.) or 5 minutes at 110° C. (230° F.) to kill them. Arloing, Cornevin, and 

 Thomas^ found that spores of B. chauvoei, if dried, resisted boiling for nearly 2 hours, 

 whereas in the moist state they did not resist boiling for more than 2 minutes. In this 

 connection Zettnow's^ observations on the resistance of spores to dry heat are of inter- 

 est. He reported viable organisms in lime paste from a sugar factory after heating for 

 30 minutes at 3io°-32o° C. (590°-6o8° F.). These organisms grew readily at 37° C. but 

 did not grow at s8°-59° C. He also claimed that spores from the lime paste which had 

 been dried on silk threads survived from 20 to 25 hours in live steam. On retesting 

 the original material, which had been stored in a paper carton in a sealed room for 

 six months, he observed that the organisms were killed below 199° C. (390.2° F.). Sim- 

 ilar material, secured from twelve places in the same sugar factory about a year later, 

 was found to be sterile after 30 minutes' exposure at 220° C. (428° F.). 



An extensive literature dealing with this subject has accumulated, and it is impos- 

 sible in this chapter to review adequately many important papers. The reader is, there- 

 fore, referred to the bibliographies and summary which have been prepared byMagoon.-i 



Morrison and Tanner^ have compiled the thermal relations and thermal death- 

 points of a large number of thermophilic spore-bearing organisms which have been 

 described by various investigators. They show a wide variation, some being destroyed 



' Cited by Morrison, L. E., and Tanner, F. W.: J. Bad., 7, 358. 1922. 

 ^Ibid., p. 359. 1922. 



^Zettnow, E.: Cenlralhl.f. Bakteriol., Abt. I, Orig., 66, 131. 1912. 

 ^Magoon, C. A.: J. Bad., 11, 253. 1926. 

 'Morrison L. E., and Tanner, F. W.: op. cit., 7, 346-53. 1922. 



285 



