CODE-SCRIPT OF BIOLOGICAL HIGH POLYMERS 121 



his collaborators of a specific deoxypentose nucleic acid as the 

 agent responsible for bacterial transformation^^, has placed the 

 nucleic acids, or at any rate the deoxypentose nucleic acids, very 

 near the gene of the geneticist. If then these nucleic acids are, 

 indeed, the genetic determinants, or form part of these systems, 

 one could ask in what manner their biological functions can be 

 translated into chemical structure, for translation there must be. 

 Two possibilities suggest themselves. (1) Each nucleic acid chain, 

 containing, perhaps, 10,000 or more nucleotides in a row, carries 

 many single determinants. But then each gene could hardly be 

 represented by a simple oligonucleotide sequence, say, a tri- or 

 tetranucleotide, since it is highly improbable statistically that such 

 sequences could be unique. (2) Less implausibly, each gene is 

 represented, or determined, by a separate nucleic acid which is a 

 distinct chemical entity, the quite well established constancy of 

 composition of the total deoxyribonucleic acid of a cell being 

 merely the statistical consequence of the unchanging character 

 of the cell. In this case, a genetic determinant, defined by a 

 characteristic chemical structure, would be unique if no two 

 nucleic acid molecules, within the same cell, were identical. I 

 have mentioned this possibility of nonidentity before^^, and it 

 actually is not such an unreasonable assumption: a haploid 

 nucleus containing, let us say, 3 • 10— ^^ g of deoxypentose nucleic 

 acid^^ would carry 300,000 molecules of nucleic acid of molecular 

 weight 6-10^ and correspondingly fewer if a higher molecular 

 weight is taken. The great difficulty in such speculations is to 

 reconcile the position of people for whom the gene is like a state 

 of mind with that of others for whom it is a substance. Who 

 would ask himself how many memories he has of the same event? 

 It has, in fact, been possible, first in our laboratory^^, to frac- 

 tionate total deoxyribonucleic acid preparations into a series of 

 regularly graded fractions of decreasing guanine and cytosine, 

 and rising adenine and thymine contents, but all showing the 

 pairing principles that I have mentioned before. The method 

 used by us was the fractional dissociation, under special con- 

 ditions, of nucleohistones or histone nucleates. If a preparation 



References p. 125 



