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.