112 FIRST STEPS TOWARDS A CHEMISTRY OF HEREDITY 



be all chemical, just as on another plane it is all physical, the 

 translation of the concept of specificity into the terms of our 

 science remains extremely difficult. 



If we compare a Staphylococcus with an E. coli cell or a sea 

 urchin egg with a mammalian ovum, comparative biochemistry 

 would probably tell us that many of their metabolic reactions, 

 many of their enzyme systems, are quite similar. Yet, how dif- 

 ferent is the whole! It must be confessed that there does not yet 

 exist a good and all-embracing biochemical explanation of speci- 

 ficity. If we look at a cat and a mouse, we know that they are dif- 

 ferent — and they themselves certainly know it even better. But 

 when we start to analyze them, we shall find much that is similar 

 and so very little that is different. It is almost as if we tried to 

 get at the meaning of "time" by taking apart a clock. There can 

 be little doubt that comparative biochemistry is barely in its 

 beginning and that, if it has difficulty in defining the differences 

 between genera, let alone species, it is hardly equipped to deal 

 with the distinction of individuals^. The biology^ and immunology 

 of individuality^ are much further advanced. It would be nice if 

 this were merely another way of saying that we shall have to 

 descend into nature by a few more decimals. But I am not certain 

 whether a radical change in the direction of our efforts will not 

 be necessary. 



In any event, a biochemist meditating on the chemical basis of 

 cellular specificity will be led directly to the concept of chemical 

 specificity. He will assume — and I believe correctly — that dif- 

 ferences in the observable behavior of cells must rest on differ- 

 ences in their chemical make-up and in the relative location of 

 the interlocking cellular elements within the meshwork of the 

 cell. As concerns the plastic constituents of the cell (proteins, 

 nucleic acids, polysaccharides, lipids), the existence of important 

 specificity characteristics within the groups of proteins and 

 polysaccharides had been revealed by immunological studies long 

 before organic chemistry had advanced to a point where chemical 

 differentiation became possible. It took even longer for the 

 chemical distinction of nucleic acids of different origin to become 



