288 DETERMINATIONS OF THERMAL DEATH-TIME 



temperatures; the age of the culture at which spores are ripe and, therefore, most resistant; 

 the reaction of the medium in which the spores are boi!ed or steamed, because all of these 

 variable factors have probably entered into the experiments. In the case of nutrient gelatin, 

 which has been a favorite medium, I find sporulation very feeble and involution forms com- 

 mon. It is quite probable that such cultures would resist boiling but feebly. The use of 

 dextrose in fairly large amounts, such as one or two per cent, has been frequent among 

 bacteriologists, although this amount is inimical to rapid spore formation." 



THE DESTRUCTION OF THE SPORES OF CI. botuUnum 



Equally interesting on account of the many discrepancies in the published data are 

 the recent heat-resistance studies on the spores of CI. botulinum. 



Van Ermengem' stated that the spores of this bacterium are considerably less heat 

 resistant than are those of the other anaerobic bacilli known to the bacteriologists of his 

 time. They were destroyed at 80° C. for 30 minutes, 85° C. for 15 minutes, or by boiling for 5 

 minutes. Von Hibler^ reported many years later varying resistance to heat, based on a study 

 of three strains of CI. botnlimim produced in different media. In one case a 4-day brain cul- 

 ture survived 3 hours at 100° C. (212° F.). 



Burke^, using ten American strains (probably CI. parabotnlinum Bengtson),'' concluded 

 that autoclaving at 15 lb. (121.3° C.) for 10 minutes is insufficient to destroy the more 

 resistant spores of this anaerobe. Thom, Edmondson, and Giltner^ tested the heat resistance 

 of cultures of the Boise asparagus strain and found that they survived 100° C. for i hour but 

 failed to grow in subcultures from tubes heated for 2 hours. In a series heated under pressure, 

 growth occurred in 50 per cent of the tubes autoclaved at 10 lb. for 15 minutes, but no growth 

 was observed after 15 lb. for 15 minutes. Weiss* found that the Boise strain survived 210 

 minutes at 100° C. (212° F.) but was killed in 240 minutes, survived 16 minutes at 105° C. 

 (221° F.), but was killed in 24 minutes and in 3 minutes at 120° C. (248° F.). Working with 

 sixteen strains he concluded that it is evident that under the best conditions for survival 

 the most resistant spores of CI. hotulinuni will be destroyed within 5 hours at 100° C, within 

 40 minutes at 105° C, and within 6 minutes at 120° C, whereas the greater number of them 

 will not survive 3 minutes. 



Dickson and his associates' report marked variations in the heat resistance of forty 

 American strains showing a survival period varying from 30 to 375 minutes at 100° C. Table 

 I gives the maximum thermal death-times for spores heated in sealed tubes in different media 

 and at different temperatures. The times include a lag period of from 2\ to 4 minutes in each 

 case, 



Esty and Meyer, and Esty,^ found the spore resistance of 112 strains of CI. bolidinum to 

 vary from 3 to 75 minutes at 105° C. The maximum survival times of such spores heated in a 

 phosphate solution, pH 7.0, was found to be 330 minutes at 100° C. (212° F.), no minutes 

 at 105° C. (221° F.), 33 minutes at 110° C. (230° F.), 11 minutes at 115° C. (239 F.), and 4 

 minutes at 120° C. (248° F.). 



' Van Ermengem, E.: Ilandb. der path. Mlkroorg. (2d ed.), 4, 909-38. Jena, 1912. 



= von Hibler, E.: loc. cii. ^ Burke, G. S.: J. A.M. A., 72, 88. 19 19. 



4 Bengtson, I. A.: Hyg. Lab. Bull. 136. 1924. 



sThom, C, Edmondson, R. B., and Giltner, L. T.: J. A.M. A., 73, 907. 1919. 



6 Weiss, H.: /. Infect. Dis., 28, 70. 1921. 



7 Dickson, E. C, Burke, G. S., Beck, D., Johnston, J., and King, 11.: J.A.M.A., 79, 1239. 1922; 

 Dickson, E. C, Burke, G. S., Beck, D., and Johnston, J.: /. Infect. Dis., 36, 472. 1925. 



8 Esty, J. R., and Meyer, K. F.: loc. clt.; Esty, J. R.: Am. J. Piih. Health, 13, 108. 1923. 



