Discussion 



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by a chemical operation in which all the soluble components are ex- 

 tracted with cold perchloric acid. I should like to ask how big a piece 

 of DNA would be precipitated by, say, cold • 2 N-perchloric acid. 



Cohn: I should say from four nucleotides onwards you are running 

 into danger of such precipitation ; and since DNAse does leave pieces of 

 four, five and six nucleotides, there could be DNA polynucleotide in 

 such a precipitate. 



Spiegelman: In that case, my conclusion is strengthened. The data 

 reported are based on the chemical analysis of the precipitate. It 

 would suggest that I don't have anything larger than four nucleotides. 

 It would appear then that I must have broken the DNA down into very 

 small pieces. 



Cohn: Yes, if there is nothing in the precipitate. 



Spiegelman: We do look in the precipitate. We give an enormous dose 

 of DNAse, in order to get the treatment through in time. It should 

 degrade very fast if it is going to go at all. 



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