I was then faced with this business of finishing my thesis in… in the two years, and this I did; I did the experimental work – I actually did repeat Delbrück and Luria's experiments. I did manage to convince Sir Cyril Hinshelwood that mutations were there. I did impress upon him the difference between impotence and chastity, which of course remains the most important thing that you can discover in science, and I finished this… I did a lot… I learnt a lot of… of... biochemistry – that again self-taught. I managed to synthesise more compounds and I didn't know what I was going to do. Now in the middle of my last year, because I... I had got the 1851 Scholarship, I had to go back to South Africa. So as far as I was concerned it looked as though, come the end of my DPhil – that would have made it 1954 – I would have to return to South Africa where a lectureship in the department of physiology had been arranged for me. In the beginning of 1954 Demerec, who was then Director of Cold Spring Harbor and a very remarkable man, arrived in Oxford, and he came to see me because he had connections with Hinshelwood, and he came to see me and he began… he got very excited by what I was doing, which you understand was heretic… heretical. Someone working on actual mutations. And I know this because he got up and closed the door of the lab before he started to talk. So he got very excited and he said, 'Won't you come to Cold Spring Harbor?' And he would arrange… help arrange a Carnegie Corporation Travelling Fellowship, which he did, and that gave me four months… four to five months in America. My family then returned to South Africa, and I went to America to spend the summer in Cold Spring Harbor and that was… that is where I really got injected into the whole of modern science.