446 HAROLD F. BLUM 



ings. For example, wavelengths shorter than about 320 m/x may 

 cause damage to any living material. This is often attributed to 

 the fact that these wavelengths are absorbed by, and cause changes 

 in, two extremely important components of living systems, proteins 

 and nucleic acids. Action spectra for these effects have been very 

 carefully measured in numerous instances, yet they often leave much 

 to be desired as regards interpretation because of factors that are 

 unknown or cannot be taken quantitatively into account. In some 



200 250 300 350 



WAVELENGTH, m/i. 



Fig. 8. Action spectra for killing of a bacterium (B) and a fungus (F) com- 

 pared to absorption spectra of nucleic acid (.V) and of a protein (P). Ordinates 

 (units chosen arbitrarily to bring the maxima to a common value) for action 

 spectra are 1/h and for absorption spectra log (T/la). Original references are 

 cited in (12a). 



cases there is good agreement with the absorption spectra of the 

 above-mentioned substances {e. g., Fig. 8); but unfortunately for 

 the clarity of the picture, there are a great many substances that 

 absorb in this same region, e.g., almost any compound containing a 

 phenolic ring. Moreover, precursors of the antirachitic vitamins (D) 

 absorb here and are activated by the same wavelengths, although the 

 action spectrum for antirachitic action shows characteristic cUfferences, 

 consistent with the differences in the absorption spectra of these sub- 

 stances, from those of proteins and nucleic acids (compare Figs. 8 



