THE SYNTHESIS OF PROTEINS 33 



tion is small. Interpolating from Fig. 2 again, it is found that if the 

 reaction is started with i per cent of the final quantity, 3.4 minutes are 

 required to produce 95 per cent, whereas if it is started with 5 per cent 

 about 2.5 minutes are required, while 10 per cent requires 1.8 minutes. 

 This variation is greater than that actually found by Delbriick and 

 Luria for the total elapsed time, but the variation in the time of forma- 

 tion itself may be greater than is indicated by the variation in ob- 

 served time. In other words, the observed time is the time required for 

 the virus to be formed plus the time required for it to be liberated 

 from all the infected cells; Tabs. = Tform. + Tub.. If an appreciable part 

 of this time is required for liberation to occur, then relatively large 

 changes in formation time would cause only slight variations in the 

 total observed time. Information in this connection could be obtained 

 by titrating the phage by the dynamic method (Krueger, 1930), which 

 determines the actual quantity present and not simply the number of 

 infective centers. 



4. The results obtained with a mixture of viruses may be explained 

 in a similar way. The first virus added increases so that by the time the 

 second virus is added, more or less of the precursor is used up. The rate 

 of formation of the second strain will then be in proportion to its con- 

 centration (assuming equal rates of reactions), so that if 50 units of 

 virus A had been formed at the time one unit of B was added, ap- 

 proximately 50 times as much A as B would be formed subsequently. 



This mechanism differs from that of Delbriick and Luria principally 

 in that it predicts that a cell can produce both strains simultaneously, 

 whereas Delbriick and Luria's hypothesis predicts an all or none result. 



The data actually show that both viruses are produced by the culture, 

 but this is explained by Delbriick and Luria as due to production of the 

 different viruses by different cells. Anderson (1942) found that chick 

 embryo cells may contain inclusion bodies of two viruses. Sylverton and 

 Berry (1936) have reported similar results. It is quite certain that some 

 cells, therefore, may produce two viruses simultaneously. 



5. In experiments with partially inactivated virus Luria and Delbriick 

 (1942) found that exposure to ultraviolet light changes the virus so 

 that it no longer produces lysis, but it still stops bacteria growth and 

 prevents formation of the active form of the same or of another virus. 



The inactivated virus does not increase. This result may be due simply 

 to the fact that the bacteria do not grow in the presence of the inacti- 

 vated virus, since anything which stops bacterial growth generally stops 

 virus formation. 



