124 FIRST STEPS TOWARDS A CHEMISTRY OF HEREDITY 



cleic acid chain which goes beyond what mere constituent 

 analysis can do. I show in Table 27 a small selection of results 

 obtained with three preparations that are indistinguishable ana- 

 lytically. 



It would take me too long to discuss all the implications of this 

 work, but I may state the principal findings. (1) Analytically in- 

 distinguishable nucleic acid specimens from different cellular 

 sources exhibit entirely different sequence characteristics. (2) In 

 no case is the nucleotide sequence that to be expected from a 

 random arrangement of monomers. (3) At least 70% of the 

 pyrimidines, and therefore 70% of the purines, occur in tracts of 

 at least three of one kind, i.e., three or more purines followed by 

 three or more pyrimidines, etc. This has a curious consequence 

 in that it restricts the number of possible permutations, though 

 this figure is still enormous. For example, a calf thymus deoxy- 

 ribonucleic acid consisting of 10,000 nucleotides (molecular 

 weight 3-10^) could exist in more than 10^^^^ isomers. With the, 

 admittedly oversimplifying, assumption that it consists of trinu- 

 cleotide tracts of one kind, i.e., adenine-adenine-adenine, etc., the 

 figure for permutational isomers drops from 10^^^*^ to 10^^^^. 

 But you will agree even so that the nucleic acids may, in their 

 sequences, contain enough code-scripts to supply a universe with 

 information. 



But do we have enough intelligence to read the information 

 thus offered to us? Not yet, at any rate. There are people who 

 suffer from giddiness when watching the Milky Way for a long 

 time on a clear night. Such people should not look into the cell 

 nucleus. Where else is there so much in so little? And beyond the 

 range of our perception, this millimicrocosm does not end, but 

 there begin galaxies of invisibility. Still, I say to those who come 

 after us: Scibitis, you shall know! But only then will the real 

 search begin. In a short time, in a very short time, our science 

 has built a ladder into the heavens; but the first two or three 

 rungs are missing. Let us hope that they will be found in the 

 next hundred years. 



