Every science has its characteristic temptation. Physics is tempted to
suppose that the universe is simple; history, that it is significant; and
biochemistry - the youngest and most self-confident of the experimental
sciences - is tempted to suppose that it is finished. One need only open a
modern compendium to see the shape of the temptation: here are the pathways,
neatly engraved; here the enzymes, each with its number; here the genomes,
each with its address. The whole of life, it would appear, has been filed. The
present treatise is written in the conviction that this appearance, though a credit
to the industry of a hundred years, is a little premature - and that a subject so
young ought not yet to speak of itself in the past tense.
What, then, is attempted here? Not an encyclopaedia, for the world has
excellent ones, and an encyclopaedia is by its nature a cabinet in which the
objects have ceased to touch one another. Not a laboratory manual, for hands
are taught in laboratories and not in prefaces.