PURPOSE 5 



under as mild conditions as possible and with the avoidance of 

 enzymic degradation, represent fibrous structures of high molec- 

 ular weight has often been demonstrated. No agreement has as 

 yet been achieved on the order of magnitude of the molecular 

 weight, since the interpretation of physical measurements of 

 largely asymmetrical molecules still presents very great difficul- 

 ties. But regardless of whether the deoxyribonucleic acid of calf 

 thymus is considered as consisting of elementary units of about 

 35,000 which tend to associate to larger structures'^- '^ or whether 

 it is regarded as a true macromolecule'^ of a molecular weight 

 around 820,000, the fact remains that the deoxypentose nucleic 

 acids are high-molecular substances which in size resemble, or 

 even surpass, the proteins. It is quite possible that there exists a 

 critical range of molecular weights above which two different 

 cells will prove unable to synthesize completely identical sub- 

 stances. The enormous number of diverse proteins may be cited 

 as an example. Duo non faciunt idem is, with respect to cellular 

 chemistry, perhaps an improved version of the old proverb. 



3. PURPOSE 



We started in our work from the assumption that the nucleic 

 acids were complicated and intricate high-polymers, comparable 

 in this respect to the proteins, and that the determination of their 

 structures and their structural differences would require the 

 development of methods suitable for the precise analysis of all 

 constituents of nucleic acids prepared from a large number of 

 different cell types. These methods had to permit the study of 

 minute amounts, since it was clear that much of the material 

 would not be readily available. The procedures developed in our 

 laboratory make it indeed possible to perform a complete con- 

 stituent analysis on 2-3 mg of nucleic acid, and this in six paral- 

 lel determinations. 



The basis of the procedure is the partition chromatography on 

 filter paper. When we started our experiments, only the quali- 

 tative application to amino acids was known'^. But it was 



References p. 23 



