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[vol. 59 



(4) Group of lines 434 irijLi of the mercury arc. Lamp H-5. Filter: 2 cm CuS04- 

 5H2O, 25 g + 300 ml ammonium hydroxide (d = 0.88), made up to 1 liter 

 with water; 1 cm NaNOo, 75 g in 100 ml water. 



(5) Band around 500 m^u (between 480 and 520 myu, center 500 m/z). Pro- 

 jection lamp with ribbon filament. Filter: Wratten no. 47, Wratten no. 58, 2 cm 

 CUSO4, 5 per cent. 



(6) Line 546 m/x of the mercury arc. Mercury discharge lamp H-5. Corning 

 glass filter combination, nos. 3484, 4303, 5120. 



Relaf-ive Lighi- In+ensH-y (arbii-rary unH-sy 



Figure 5. The PHTR rate as a function of the intensity of the reactivating light. The 

 PHTR rate is expressed in sec~^ and the light intensity in arbitrary units. Phage T2r was 

 irradiated for 20 seconds with the germicidal lamp, adsorbed on resting bacteria, and il- 

 luminated in liquid at 37 C. 



(7) Group 576-579 m/n of the mercury arc. Lamp H-5. Filter: 1 cm mixture 

 of CuCl2-2H20, 10 g in 10 ml water and CaCls, 3 m, 90 ml; 2 cm KoCrjO?, 15 g 

 in 200 ml water. 



The efficiency of the different lights was determined in the following way: 

 For each light the range of intensity w'as first determined, in which the PHTR 

 rate is approximately proportional to the light intensity; the intensity of the 

 most effective wave lengths was reduced by filters until it fell into this range. 

 The rate of PHTR was then determined for each wave length, and the relative 

 intensities were measured with a thermopile. The time of illumination was short, 

 so that the amount of PHTR was very nearly proportional to the dose of reac- 

 tivating light (see previous section). 



The dose of light of each wave length necessary to give a standard amount of 



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