Then we had to purify the enzyme. Well, in those days, there were not so many techniques for purifying protein enzymes and one of the simplest techniques was what is known as isoelectric precipitation, which takes advantage of the fact that proteins are least soluble when their electric charge is zero. And so you acidify the medium and you reach a pH where many proteins will precipitate because of this lack of electric charge. And so at pH five we got a big precipitate and our enzyme was there in the precipitate. So that was the first step: a very dirty precipitate, obviously. And so the next step was, of course... if this was isoelectric precipitation, was to re-dissolve the enzyme and try something else, like ammonium sulphate precipitation or alcohol precipitation which were the only techniques available at that time. Chromatography was not known yet, or at least not for proteins. And so we took our precipitate, changed the pH back to seven; enzyme would not re-dissolve. So this was not the reversible kind of reaction that you have with iso-electro precipitation; this was an irreversible agglutination, which implied that the enzyme was probably associated with some kind of cell structure. It so happens that on my return from the United States... some time before that, I had visited a few labs and I had visited the best: the discoverer of insulin in Toronto; I had visited a man called Levine in Chicago because he'd worked on insulin and liver; I'd visited Lipmann in Boston because he was one of my heroes – Lipmann the father of bioenergetics. I was so impressed with this work, and I found it so beautiful I went to see him. You know, amazingly, I wouldn't do this anymore... today; a young student would come to me and say, 'I want to see you because I admire you'; I would say, 'Well I have more interesting or important things to do.' No, he actually... he saw me, talked with me, even invited me and my wife to a Chinese restaurant. So I had a lovely time in Boston – finally ended up in New York where I went to the Rockefeller Institute for Medical Research.