Scott Weaver- Rolling Through The Bay

intricacy

If you analyze a molecule of chlorophyl itself, what you get is
one hundred thirty-six atoms of hydrogen, carbon, oxygen and nitrogen
arranged in an exact and complex relationship around a central ring.
At the ring's center is a single atom of magnesium.

Now: If you remove the atom of magnesium and in its exact place
put an atom of iron, you get a molecule of hemoglobin.
The iron atom combines with all the other atoms to make red blood,
the streaming red dots in the goldfish's tail.

-Annie Dillard Pilgrim at Tinker's Creek