One of the important stages in penicillin, which was during that year, took place during the X-ray analysis group meeting. When we decided to let Charles Bunn work on the sodium salt with us, and brought him into the collaboration. But we also were very anxious to arrange for better computing, particularly of the three-dimensional data, because we thought from a three-dimensional Patterson we might be able to get the structure straight away. And Charles... this somewhat odd character, Comrie, who had a computing firm, came through, and he discussed what we needed, because he said, of course, if we had suggested we only needed to calculate certain lines in the density to get what we knew, but he said, if you had the whole three-dimensional map, it would, of course, be much easier to calculate that. So I said, 'Well, we'd much rather have the whole three-dimensional map'. So then they got £1000 from the MRC [Medical Research Council], which they always thought was much too expensive, to get the punch cards made to enable the three-dimensional series to be calculated.

[Q] Now, when was that, Dorothy?

That was now getting on, when the X-ray analysis group was somewhere about April or thereabouts.

[Q] In '40...?

 '45

[Q] '45. Right.

Yes. So Comrie went ahead with his organisation making the punch cards necessary. So we thought that if we finish the structure by ordinary criteria, I mean, put in enough hours and the rest of it, by May 1945 when we had the three projections. And Charles, of course, separately refined the sodium salts, so he had comparable...

[Q] Detail?

... details agreeing with ours. Well, then we didn't, we really felt we knew the structure before the three-dimensional cards came into our hands at all, but it seemed a pity not to use them, so we thought the obvious thing was to calculate the three-dimensional electron density, and it would enable us to refine the structure a little, and also check it. So, if we wanted to, we did this by having two calculations carried out, and that's what I think you're remembering. If we had one calculation we believed in, in which the...

[Q] All the atoms were put in?

... all the atoms were put in, as we thought they were, and then a second calculation, in which the beta-lactam atoms were moved into positions more corresponding to the oxyacetylene ring. And from the results there was no doubt at all that it was the thiazolidine and beta-lactam ring. But we generally had the molecules, the structure, from the moment we had the three projections. But, on the other hand, the setting up of the three-dimensional model on glass plates, is also historic. Because, although people don't now always make these models of their simple molecules, they make them of their complicated ones.