56 LOGARITHMIC ORDER OF DEATH 



But, as Hastings, Fred and Carroll (1925) remark, "one 

 million spores should include all grades of heat resis- 

 tance." Then in the 900 million suspension of Table 9 

 there should be no spore which is more resistant than 

 those in the 9 million suspension. Accordingly, though 

 the suspension with 900,000,000 spores survives 12 min- 

 utes longer than the one with 9,000,000, this difference 

 cannot be explained by a graded resistance. The assump- 

 tion that death is caused by the inactivation of a single 

 molecule per cell fits the facts perfectly. 



This influence of very large numbers of individuals 

 should make itself felt also in higher organisms. In 

 Table 4, for instance, for n = 4, it was computed that 

 after 5 minutes, 1 out of 10 individuals is alive, after 8 

 minutes, 1 out of 100, after 12 minutes 1 out of 1,000 and 

 after 15 minutes 1 out of 10,000. As n increases, the ab- 

 solute time differences remain the same, although their 

 effect is relatively smaller. Actual experiments with 

 very large numbers of higher organisms are not known 

 to the author. Possibly some investigations on the via- 

 bility of seeds have been made which would give infor- 

 mation on this point. 



8 el e ct i n \o f Resistant Strains. Bac- 

 teria can become accustomed, to a certain degree, to ad- 

 verse conditions, and strains of remarkable resistance 

 do occasionally occur. If the last survivor is the most 

 resistant, it should be easy to produce such a resistant 

 strain by simply propagating the last survivors from a 

 large number of exposed bacteria. However, if the death 

 of the cell results from a lethal mutation, the last sur- 

 vivor is not different from the bacterium which is the 

 first to die (see page 40). 



Several attempts to obtain resistant strains from the 

 last survivors have been published, and in most cases, 

 failure was reported. One of the most extensive and 

 persistent attempts is that by Gage and Stoughton (1906) 

 who tried to obtain a heat-resistant strain of Bacterium 



