AMPLICATIONS AND SOURCES OF ULTRAVIOLET 



47 



Fig. 2-5. Relative energy distribution of (a) high- and (6) low-pressure mercury arcs, 

 transmission of arc tube glasses, and action curves. 



SUSCEPTIBILITY TO ULTRAVIOLET 

 INJURY, MUTATION, AND KILL 



An understanding of the biophysical nature of cell injury, mutation, 

 and kill is not essential for the practical applications of the ultraviolet! 

 In this discussion, for practical purposes, an organism is considered dead 

 when it is unable to reproduce. The possibility of this being a condition 

 far short of complete destruction, and the logarithmic nature of ultra- 

 violet killing, leave considerable uncertainty as to just when all the organ- 

 isms in one group are dead. In most of the practical ultraviolet applica- 

 tions a complete kill is not necessary, but whenever it is necessary it can be 

 pro\'ided by adequate factors of certainty in exposure. 



There is ample evidence from practical experience that the growth of 

 fuiigi can be prevented by exposures of the order of those effective for bac- 

 teria killing and by exposure of only a fraction ( a tenth to a hundredth) 

 of those required for the killing of bacterial spores. The wilting and 

 death of common plants such as ivy and tomato under such exposures sug- 



