Linus Pauling: It occurred to me that the same magnetic methods that we had been using to study
simple compounds of iron, in order to determine the bond type, could be used to study
the hemoglobin molecule. One of my students, Charles Coryell, and I, then got some
blood, cattle blood, and put it into an apparatus. It consisted of a balance, which
we had fitted out in such a way that a wire was suspended from one arm of the balance
through a hole in the base of the cabinet, and held a tube. This tube was placed between
the poles of an electromagnet. We filled it with blood, oxygenated blood, and balanced
it to measure its weight. Then we passed an electric current through the coils of
wire and the apparent weight changed.
It turned out that the blood was being repelled from the magnet. When we removed the
oxygen molecules from the blood to get venous blood, the sort that flows through the
veins in the body after it has given up the oxygen in the tissues, then we found that
the blood was attracted by the magnet, attracted into the magnetic field. The iron
atom had changed the nature of its bonds with the surrounding atoms. This led to an
understanding of the nature of the structure of hemoglobin in the immediate neighborhood
of each of the four iron atoms.