MECHANISM OF DEATH 299 



This is partly due to inadequate technique. The death rates 

 for two transfers of the same culture on different days vary greatly. 

 Chick (1910) found the death rate (0.434if) of Micr. 'pyogenes 

 aureus with 0.6% phenol at 20°C. to be, on March 13th = 0.32, 

 March 16th = 0.114, March 30th = 0.32 and AprH 6th = 0.136. 

 The same author found that Bad. coli died in water of 489°C. 

 with a death rate of 0.172, and eleven days later at 49.0°C., with a 

 death rate of 0.042. Such variations (amounting in the last case 

 to 400%) are found in the work of other investigators as well (see 

 e.g., Table 82). An explanation shall be tried later (p. 333 and 

 345). It seems that in recent experiments, it has been possible to 

 reduce this error considerably. Myers (1929) was able to average 

 data from different months without difficulty. But as long as the 

 technique shows deviations within the same strain of the degree just 

 mentioned, there is little hope of proving increased resistance. 

 This may account for some of the failures. 



It is well known that bacteria can be adapted to poisons, 

 to higher temperatures or other adverse conditions. 

 This is accomplished by subjecting them to gradually 

 increasing intensities of the harmful substances, or 

 conditions. With our problem, however, we are inter- 

 ested only in those cases where the last survivors show 

 greater resistance when compared with their ancestors, 

 or with the average. 



The experiments of Magoon (1926) which are sometimes cited 

 as such an example, are not at all convincing, Magoon transfered 

 the last survivors of heated spores of B. mycoides to a new medium 

 and determined the resistance of the newly developed spores again. 

 The first culture survived nine minutes at lOO^C; how much longer 

 the spores might have Uved, was not determined. The second 

 culture survived twenty minutes; it was not ascertained how much 

 more heating it might have tolerated. Only with the third culture, 

 it was certain that it could tolerate twenty-eight, but not twenty-nine 

 minutes' heating. There is no evidence whatever that the other two 

 cultures were less qresistant. The fourth culture was tested for 

 thirty-six minutes and all survived; this culture was more resistant 



