From the 1980 lecture programme:
Haemoglobin is the protein of the red blood cells which carries oxygen from the lungs to the tissues and helps to carry carbon dioxide back from the tissues to the lungs. It fulfils this dual role by switching back and forth between two alternative structures, one in the arties and another in the veins. The structure of its four protein chains is determined by genes and mutations in these genes can make children ill by impairing the function of their haemoglobin molecules. We can now track down the causes of such illnesses to changes of a few atoms but we cannot yet cure them.