Death rate of populations of Bact. lactis aerogenes. III. Interpretation of survival curves.

Abstract

Most theories of the survival curve postulate either a progressive action of the lethal agent on cells with large inherent differences of resistance, or random events such as encounters between the agent and a sensitive region of the cells. A survey of the experimental evidence, however, suggests that death of the bacterial cell involves not only a progressive destruction of essential cell activities, but may also be conditioned at some stage by a random combina­tion of various independent events. The form of the survival curve depends essentially on the speed of the former process in relation to the probability of the latter. Factors modifying this form are: (1) intrinsic differences between individual cells, which, however, appear not to be the major cause of variation of survival times, and (2) the occurrence, in favourable circumstances, of adaptive adjustments. It is the element of chance in survival that accounts for the frequent observation of extremely skew distributions of survival times (and in the limit nearly logarithmic decline curves). It probably arises from the fact that the concentrations of various molecular species show complex fluctuations, at the appropriate phase of which certain cell activities fall below a critical level for viability.