While serving as an army medical officer in the Second World War, epidemiologist Archie Cochrane was captured in June 1941 and sent to a prisoner-of-war camp in Salonica, Greece. Conditions in the camp were appalling. Cochrane instituted a medical surveillance system, and found an outbreak of leg oedema accompanied by jaundice, from which he himself was one of the sufferers. In desperation, and vaguely remembering the phrase ‘wet beri-beri’, he decided to see if he could show that the oedema was due to a vitamin deficiency. Having managed to obtain some yeast on the black market, he recruited twenty young prisoners, cleared two wards, and numbered the twenty prisoners off: odd numbers to one ward, even numbers to the other. The men in one ward got two spoonfuls of yeast each every day, and the men in the other ward got one tablet of vitamin C. The outcome of the experiment was assessed mainly by frequency of urination, as there were no buckets available to measure volume. For the first two days, there was no difference between the wards, but by the fourth day the difference was conclusive. Cochrane conducted two simple tests: he asked the members of each ward whether they felt better, worse or the same – nine out of ten in the yeast ward said they felt better; and he watched the men walking, deciding that oedema among members of the yeast ward was less than among members of the vitamin C ward. He wrote up the results of this experiment, presented them to the Germans, and asked for more food and more yeast. The Germans produced more yeast, which Cochrane gave to the men, and the oedema disappeared. Commenting on this, ‘my first, worst, and most successful clinical trial’, at a distance of more than forty years, he observed: