The first thing we had to do was find some way to study these things. So I used — again, it’s a relatively simple idea. The idea is simple. In practice, it’s very difficult. Which was to take molecules that I had reason to believe could interact with this receptor, like beta blockers, which had just been developed, and radioactively label them and use that radioactivity as a way of following the binding, the sticking interaction of that molecule to the receptor. And then with this radioactive probe stuck to it, now I could try to isolate it, following the radioactivity as a marker. And over a period of years, we got that to work for several receptors. Then we dissolved the cell membranes, plucked the receptors out. The receptors are very rare. So for example, for every two- or 300,000 protein molecules in the cell membrane, one of them would be this receptor. So the next job was to isolate this receptor, to get rid of the 199,999 that aren’t the receptor and just get receptor. Okay, yeah, exactly. Extraordinarily difficult work, but we succeeded in doing that and showed that this one isolated molecule could do the two things that a receptor would do. First, it could bind or interact with drugs that were known to interact with that receptor. And in a way that would be predicted by the physiology. That is, if I had three things that could work on that receptor and we knew from physiological experiments that, say, drug one was better than drug two was better than drug three, then my protein should bind drug one better than two better than three. Only there weren’t just three, there were dozens. So we could test that very rigorously. So that was the first criterion. The second criterion is that binding of a drug like adrenaline to this receptor, that that receptor could now do something — stimulate the cell to do stuff. Now that was even tougher. So we came up with methods where we found cells that didn’t have adrenaline receptors. How did we know they didn’t have them? Because they couldn’t bind these radioactive probes. But they did have the response machinery, okay. Because they had receptors for other things. And then we took these receptors and by techniques that we worked out, we were able to plug them back into the outside of these cells. And now the cells responded to adrenaline. So now I knew that this pure receptor molecule that I had could do both things that you’d expect a receptor to do, interact with something like adrenaline, and do something to the cell.