250 



BIOLOGICAL EFFECTS OF IONIZING RADIATIONS 



Figure 9-8. Electron Micrographs of Normal and Gamma-irradiated E. coli Bacteria. 

 Left: Parent, shadowed at an angle of 30° with evaporated chromium metal. Note the 

 long flagellae still intact (10,000 x). Center-. A heavily irradiated (2 million rads), radia- 

 tion-resistant strain, remarkably elongated, and with terminal budding (7,000 x). Right: 

 A stained, ultrathin section of a freeze-dried sample of the heavily irradiated strain, 

 showing side budding (25,000 x). (Courtesy of I. E. Erdman and B. Kronmueller, Na- 

 tional Health and Welfare Laboratories, Ottawa.) 



unity; the plot of log (survivors) vs dose is curved, not straight, a varies, and 

 the survival expression becomes more complicated.* Thus, the results of ir- 

 radiation of multiploid yeast cells indicate very complicated kinetics — in- 

 teresting enough, and of considerable significance because of what they will 

 some day tell us about human multiploid cells under irradiation; but never- 

 theless not truly clear now, and therefore beyond our scope to discuss here. 

 The general rule-of-thumb is that for multiploids the sensitivity, a, becomes 

 higher the longer the cells are irradiated. The numbers given in Table 9-4 

 for E. coli, for example, refer to linear portions of the log (survivors) vs dose 

 curve, and therefore are only approximate. Higher up the animal heirarchy 

 the deviations from this simply law are greater, and it is best then to rely on 

 the LD 50 , not the a. 



Arranged in decreasing order of sensitivity (<x) the following cells provide 

 a broad spectrum of the general damage caused by whole-cell irradiation: 



Lymphocytes > granulocytes > basal cells** > alveolar cells of lung > bile duct 

 cells > cells of tubules of kidneys > endothelial cells > connective tissue cells > 

 muscle cells > bone cells > nerve cells. 



"One form, based on a multiple-hit theory, introduces a correction term: 



yvyA 



-oD 







(1 - c/D) 



where c is a constant. 



**Producers of specialized cells of bone marrow, gonads, intestines, sometimes called stem 

 cells. 



