EFFECT OF RADIATIONS ON PHAGE PARTICLES 65 



within 5 minutes after the suspension is placed in light. The 

 presence of 0.01 per cent cysteine gives complete protection 

 against such photodynamic action, for which also oxygen ap- 

 pears to be essential, since no inactivation takes place in the light 

 in a nitrogen atmosphere. Similar results were reported by 

 Perdrau and Todd (1933). Burnet (1933e) investigated the 

 photodynamic action of methylene blue on a series of coli-dys- 

 entery phages. He found marked differences in sensitivity, 

 differences which were correlated not with particle size but 

 rather with serological classification. Hence photodynamic 

 sensitivity, like sensitivity to visible light, is of taxonomic signifi- 

 cance, although here too the chemical basis for such differential 

 behavior is as yet unknown. Krueger Scribner, and Mc- 

 cracken (1940) reported the photodynamic inactivation of a 

 "phage precursor." In these experiments, a reduced yield of 

 phage was encountered after illumination prior to infection of 

 the host bacteria in the presence of 10~^ M methylene blue, a 

 treatment which was said not to reduce the bacterial colony 

 count. Since the assays in this experiment were made by 

 Krueger's kinetic method, it is difficult to interpret such results. 

 Illumination of bacteria in the absence of methylene blue sup- 

 presses their capacity to produce phage without killing them 

 (Dulbecco and Weigle, 1952; Latarjet and Miletic, 1953; 

 Hill, 1956). 



Yamamoto (1956) studied the relation between structure of 

 dyes and photodynamic inactivation of the T series of coliphages, 

 and observed competitive interactions between effective and in- 

 effective dyes. Welsh and Adams (1954) found that photo- 

 dynamic action on T2 destroys infectivity three times faster than 

 it destroys the host-killing property of the particles. No photo- 

 reactivation or multiplicity reactivation could be demonstrated. 



2. Ultraviolet Light 



Of all the agents capable of inactivating bacteriophages, ul- 

 traviolet light has been studied most extensively and has shown 

 the most diverse and interesting effects. Besides simply in- 



