160 THE PHYSICS OF VIRUSES 



effective. The nucleotide absorption seems to be the most 

 effective . 



Such an action spectrum, although of very great value, repre- 

 sents only one step along a road that should lead to fundamental 

 discoveries about viruses. From what has already been said, it is 

 clear that the inactivation of a virus like T-1 is a complex 

 process. It may be the result of over-lengthening of the latent 

 period, which Luria (1944) has shown to occur following ultra- 

 violet illumination, or it may be a lethal mutation in a genetic 

 element, or possibly a destruction of specific surface groups. All 

 of these various aspects of virus behavior have their separate 

 action spectra, and only when a selection of these are available 

 can the real power of the spectroscopic approach be apparent. 

 This point is illustrated by some studies by Tamm and Fluke 

 (1950) on influenza virus which are described below, 



Infectivity and Hemagglutination Action Spectra of 



Influenza Virus 



The infectivity and hemagglutinating ability of PR-8 in- 

 fluenza virus can both be readily studied. The former is meas- 

 ured by inoculating 10-day-old embryonated eggs and deter- 

 mining whether the inoculum results in a strong rise in virus in 

 the egg due to active infection. The dilution at which this will 

 occur is a measure of the activity of the virus. Hemagglutination 

 is measured in a somewhat similar way by making twofold dilu- 

 tions until one dilution fails to produce definite agglutination of 

 red cells. 



Tamm and Fluke employed monochromatic ultraviolet light 

 of four wavelengths. The virus was irradiated in a gold-plated 

 cell with quartz windows on two sides. Radiation intensity on 

 both sides of the cell was measured by a phototube which was 

 calibrated by means of a thermopile. Exposures were made for 

 various times at known intensities. 



The results are indicated in Fig. 6.9. The wavelength region 

 covered is somewhat limited, notably in stopping short of the 

 polypeptide absorption region, but it is clear that the maximum 

 effect on infectivity is nearer to a nucleic-acid maximum, and is 



