162 D. Wright Wilson 



with the maximum incorporation of radioactivity in the DNA 

 pyrimidines of the virus. Thus as the DNA of the virus 

 increased 4 times (from 0-048 to 0-208) the specific activity 

 of each of the DNA pyrimidines was reduced to one-quarter. 

 The experiments are not in agreement with the idea that the 

 host furnishes a definite amount of its preformed DNA to 

 each virus particle. They may be explained by saying that 

 the virus DNA is formed from the total available pool of 

 material, which diminishes in radioactivity as more DNA is 

 synthesized. 



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DISCUSSION 



Hammarsten: We recently tried orotic acid on liver slices and found 

 that part of it was incorporated in the pyrimidines. Of course, a large 

 part was combusted, and the part escaping combustion and incorporation 



