BOTULISM AND HOME CANNING 19 



Oxygen 



Although CI. hotidinum is considered to be a strict anaerobe it seems to be able 

 to tolerate a little oxygen. Dack, Starin and Werner (1927) stated that an oxygen 

 pressure of 5 cm. completely inhibited this organism. Meyer (1929) reported 

 that CL parabotulinum Type A and Type B failed to grow when the oxygen 

 tension exceeded 1.14 cm. and 1.36 cm. or 7.16 and 8.6 percent, respectively. 

 In another publication Dack and Baumgartner (1928) indicated that, when CI. 

 botulinum Type A was grown in veal infusion broth under reduced oxygen pres- 

 sure, no growth was obtained when the pressure was greater than 1.3 cm. As 

 the oxygen pressure increased from 0.1 cm. to 1.3 cm. the time of growth became 

 more irregular. 



Salt and Sugar 



Experimental data reported by various research workers indicate that CI. 

 botulinum can tolerate relatively large concentrations of salt and sugar. Tanner 

 (1933) has suggested that statements regarding the maximum concentration of 

 salt tolerated by this organism are to be taken with considerable reservation, as 

 the inhibiting concentration of sodium chloride seems to be influenced by the 

 medium in which the experiments are carried out. In general a 10 percent con- 

 centration of salt would appear to inhibit the growth of the organism under most 

 conditions. 



Available reports indicate that sugar, except in high concentrations (greater 

 than 55-64 percent), is not always effective in inhibiting the growth of CI. botu- 

 linum. 



Effect of Heating on Dormancy of Spores 



Of particular interest in regard to home-canned foods is the effect of heating 

 on the dormancy- of the spores of CI. botulinum. Dickson (1928) reported that 

 spores which had been subjected to heat in a broth covered with a thin layer of 

 oil within sealed glass tubes exhibited a marked dormancy. Positive tubes con- 

 tinued to appear from time to time for 75 months after the first tubes were heated 

 and 67 months after the heating experiments were stopped. According to Burke 

 (1923) spores which reproduce after long periods of dormancy are capable of 

 producing typical and strong toxins. 



Thus it would appear that home-canned foods ma\ become toxic after long 

 months of storage even though they were non-toxic for some time after canning. 

 Warm storage conditions would tend to favor the development of dormant spores. 



Temperature 



Like other living things the spores of CI. botulinum have an optimum tempera- 

 ture for growth and development. Although 71.6°F. (22°C.) has often been 

 considered the optimum temperature for this organism, some data have been 

 reported which show that growth and toxin production may occur at 98. 6T 

 (37°C.). 



Tanner and Oglesby (1936) made a comprehensive survey of the literature on 

 the effect of temperature on the growth of CI. botulinum. Because little work had 

 been done in the range of temperatures between freezing and room temperature 



