One of the things that you want when you're doing a lot of genetics is, in fact, to be able to store them and... to store clones of these animals. With E. coli [Escherichia coli] it was very easy. We just froze them in glycerol. And just put them away like this. So that you could keep this tremendous inventory of different clones. It's one of the... it's one of the databases geneticists want, is to be able to go and find mutants. Phage was perfect, you just keep it in little bottles, a drop or two is enough, so it doesn't take much room. Of course, if you work with mice you've got to keep on breeding them, it's very hard to store. And so we wanted some way of storing these genes, we didn't want to keep on propagating them, because that becomes an enormous labour. And fortunately we very... it was discovered by John Sulston I was doing these experiments as well, I hadn't had much luck, and he discovered that, that if you... the book said that if you froze nematodes, froze anything in liquid nitrogen... of course it was very interesting of... of storage, it's cryogenics and, of course, everybody wants to store things, and we quickly learned that it's very easy to put... to freeze things in liquid nitrogen, it's thawing that's the problem, and there are lots of papers on how you do this with... with people, but we hadn't heard of anybody who'd been successfully thawed, you see. Because, of course, they didn't do it with live people. So what we found was that when you store cells in liquid nitrogen you're supposed to thaw them very rapidly. And... and that was the thing and you're supposed to freeze them rapidly. But we found that if we froze them slowly and thawed them, then this was the best way to do it. And so by slow freezing, about a degree a minute, you could in fact preserve these animals and thaw them and have them come alive. And that was one of the signal advantages of this. Whenever one goes into research on these things there's always these things that happen. If you work long enough you'll always find by dint of trying many things or looking for many things that these... these technical things emerge. And that was a great advantage of these.