20. Conclusion 



After having been submerged in details through nineteen 

 chapters, we may conclude by coming to the surface in order to 

 look around, find our bearings, and ask what all this was about. 



Going back to our point of departure, to the "chiaroscuro," we 

 should see its outlines somewhat clearer now. Biochemistry is not 

 an independent principle; it is dependent for its advance on prog- 

 ress made in other fields; in the first place in pure chemistry. There 

 are definitely two periods discernible in the history of this science. 

 The first was heralded by Lucretius and Epicurus, who professed 

 that matter was built of small, indivisible units, atoms. What 

 chemistry has done in the subsequent two milleniums has been, 

 essentially, to find out how many different sorts of atoms there are 

 — about a hundred — to isolate them, name them, and establish 

 the ways and forms in which they are linked together. The dif- 

 ferent atoms have been symbolized by letters, their links by dashes, 

 so that by means of letters and dashes we can write symbols on 

 paper which give a fairly clear picture of the structure of complex 

 molecules. 



Biochemistry, following in the footsteps of chemistry, has been 

 wonderfully successful in analyzing structures and reactions which 

 could be described in these terms and by their symbols, by letter- 

 dash-letter (as P — O — P), following up the various atoms and 

 bonds in their way through the maze of biological reactions. 



The second step of the history of chemistry was heralded by 

 Bohr and his orbits in 1913. The theory came of age in 1927 with 

 Schrodinger's wave equation. In this theory, the atom is no more 

 an indivisible unit, but a cloud of electrons, or more exactly, a 

 cloud of the probabilit^'-densities of electrons- Molecules are 



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