380 S. GARD AND O. MAALOE 



A second detailed study was made by Welsch and Adams (1954) with the 

 coliphages of the T series and methylene blue. Inactivation kmetics were 

 first order (with a short lag) and the rate constants varied with pH and with 

 the concentration of the dye, both factors probably affecting adsorption of 

 the dye to the phage surface. A 20-fold difference was observed between the 

 highest and the lowest inactivation rate, and, as observed earlier by Burnet 

 (1933) for dysentery phages, the sensitivity to the photodynamic effect 

 varied considerably more between than within serological groups. There was 

 no obvious correlation between sensitivity and morphological and physio- 

 logical characteristics, and all the phages tested were more or less equally 

 sensitive to hydrogen peroxide. The authors concluded that, most likely, 

 adsorption of the dye to the phage surface was the rate-limiting factor. 



Testing the effect of eosin on Newcastle virus, Torlone (1955) found that, 

 upon illumination in the presence of oxygen, uifectivity disappeared before 

 the hemagglutmating activity. Without oxygen no inactivation was observed. 



The fact that normal daylight may inactivate viruses is of considerable 

 practical mterest. Skinner and Bradish (1954) investigated the susceptibihty 

 of several animal viruses to light as a function of the intensity and duration 

 of illumination and the composition of the suspending medium. Unfiltered 

 fresh suspensions of egg-grown strains of the viruses of vesicular stomatitis, 

 influenza, Newcastle disease, and fowl plague were strongly inactivated by 

 exposure to daylight for 4 hours; foot-and-mouth disease virus was much 

 more stable. The authors did not analyze the inactivation process, except to 

 show that UV probably was not responsible. Some viruses were protected by 

 the addition of 10 % rabbit serum; in experiments with Newcastle virus, 

 cysteine was tried but no protection was observed (cf. CHfton, 1931). 



Finally, the phages C16 and S13 have been shown to be slowly inactivated 

 by near UV and by blue light in the absence of added dye (Latarjet and 

 Wahl, 1945; Wahl and Latarjet, 1947). Unlike the photodynamic effect, this 

 inactivation process was almost independent of temperature (between 17 

 and 37°C.). The influence of oxygen was not tested. In the far UV region, the 

 rate of inactivation of phage C16 was 3 times that of phage S13; in the near 

 UV region and with visible light, C16 was twice as resistant as S13, indicating 

 that the mechanism of inactivation is probably different in the different 

 wavelength regions, 



4. Inactivation Due to Decay of Incor^porated Radioactive Phosphorus 



These very special experiments are most naturally treated at this point 

 because they bear some resemblance to both X-ray and UV experiments: 

 first, because the decay process, by which the P^^atom is changed into a sulfur 

 atom, involves the ejection of a fast electron and the local release of consider- 

 able energy from the recoiling atomic nucleus; second, because it has been 



