I remember vividly the beginnings of molecular biology. For me it began when Schlesinger showed in 1934 that a bacterial virus contained thymonucleic acid—we call it D.N.A. now. Andrewes, Elford, and I were then having a happy time discovering the wide range of physical and biological properties that could be observed amongst the collection of bacteriophages I had brought to Hampstead. I forget whether it has ever been put on record that I obtained most of them on a visit to my brother's farm in Gippsland, Victoria. Cattle, pigs, and fowls all provided their samples of fresh feces, and there was a fine overall yield of phages. One of them, C13, was the first virus with a single strand D.N.A. to be observed, and it is still extant. Our favourite phage at the time was C16, now known to be almost identical with T2 and (as we found in 1933)