. Elementary biophysics: selected topics . Lag Logarithmic I l_ Maximum -stationary - I 2 4 6 8 10 Age of culture (hours) 12 Id1 Fig. 55. A replotting of some of the data of Fig. 55, showing the cycling of radio sensitivity. The cell concentration is shown as a dashed line. (From Staple- ton, J. Bacteriology, 20, 357, 1955; courtesy the author and Williams and Wilkins Co., Baltimore, Md.) numbers simply do not follow the ploidy. Another example is the varia- tion in inactivation curves of bacteria in various stages of their growth cycle. The experimental results are given in Fig. 54, taken fro
. Elementary biophysics: selected topics . Lag Logarithmic I l_ Maximum -stationary - I 2 4 6 8 10 Age of culture (hours) 12 Id1 Fig. 55. A replotting of some of the data of Fig. 55, showing the cycling of radio sensitivity. The cell concentration is shown as a dashed line. (From Staple- ton, J. Bacteriology, 20, 357, 1955; courtesy the author and Williams and Wilkins Co., Baltimore, Md.) numbers simply do not follow the ploidy. Another example is the varia- tion in inactivation curves of bacteria in various stages of their growth cycle. The experimental results are given in Fig. 54, taken from Staple- ton's work. This information can be summarized as in Fig. 55, also taken from Stapleton, which shows clearly the cyclic variation in radio- sensitivity. This variation is not altogether out of the purview of target theory, for rapidly dividing cells could well have a lesser number of nuclei than lagging or stationary phase cells in which nuclear division may have occurred without corresponding cell division. Furthermore, the metabolic activity of the nucleic acids of the nuclear apparatus could also result in different sensitivities at different times in the growth cycle. However, there still remain the problei is of a change in target number from unity to six, which seems outside any reasonable increase in nuclear number. Opponents of the use of target theory maintain that such failures show the terrible weakness of the theory, and some even go so far as to say that target theory should therefore really not be used at all. Our point of view is that since there are many instances in which target theory gives well-documented success, there is nothing basically wrong with the theory, but that where the theory fails it must be due to the
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