ACTION OF ULTRAVIOLET LIGHT ON VIRUSES 



163 



roughly proportional to the surface area of the molecule. On 

 rather slender evidence, McLaren (1951) has proposed that the 

 ionic yields for the indirect action of ionizing radiation also 

 obey this relation. 



1.0 



oTMV 



en 



oc 



n 

 \ \/-Vaccinia 



2200 2400 2600 



Wavelength 



2800 ^ 



Fig. 6.10. Action spectra for five viruses, taken from HoUaender and Oli- 

 phant (1944). The phage acts on Staphylococcus aureus. 



If this idea is right then the photons per inactivation should 

 give some idea of the size of the unit being inactivated. Far 

 too little data is at present available, but it represents an im- 

 portant region for future physical studies of viruses. The 

 quantum yield for inactivation of TMV at 2,537 A is 4.3 X 10"^ 

 (McLaren, 1950), and for T-1 phage at 2,600 A it is 3 X 10"^ 

 (Fluke, 1953). 



