4 CHEMICAL SPECIFICITY OF NUCLEIC ACIDS 



examined analytically in some detail, all conclusions derived from 

 the study of these substances were immediately extended to the 

 entire realm of nature; a jump of a boldness that should astound 

 a circus acrobat. This went so far that in some publications the 

 starting material for the so-called "thymonucleic acid" was not 

 even mentioned or that it was not thymus at all, as may some- 

 times be gathered from the context, but, for instance, fish sperm 

 or spleen. The animal species that had furnished the starting 

 material often remained unspecified. 



Now the question arises: How different must complicated sub- 

 stances be, before we can recognize their difference? In the mul- 

 tiformity of its appearances nature can be primitive and it can 

 be subtle. It is primitive in creating in a cell, such as the tubercle 

 bacillus, a host of novel compounds, new fatty acids, alcohols, 

 etc., that are nowhere else encountered. There, the recognition 

 of chemical pecuharities is relatively easy. But in the case of the 

 proteins and nucleic acids, I believe, nature has acted most subtly; 

 and the task facing us is much more difficult. There is nothing 

 more dangerous in the natural sciences than to look for harmony, 

 order, regularity, before the proper level is reached. The harmony 

 of cellular life may well appear chaotic to us. The disgust for the 

 amorphous, the ostensibly anomalous — an interesting problem in 

 the psychology of science — has produced many theories that 

 shrank gradually to hypotheses and then vanished. 



We must realize that minute changes in the nucleic acid, e.g., 

 the disappearance of one guanine molecule out of a hundred, 

 could produce far-reaching changes in the geometry of the con- 

 jugated nucleoprotein; and it is not impossible that rearrange- 

 ments of this type are among the causes of the occurrence of 

 mutations.* 



The molecular weight of the pentose nucleic acids, especially 

 of those from animal tissue cells, is not yet known; and the 

 problem of their preparation and homogeneity still is in a very 

 sad state. But that the deoxypentose nucleic acids, prepared 



For additional remarks on this problem, compare Ref. 12. 



