And I asked Bob what he was doing and he said he's working with this Eaton agent and he started to describe... I had heard of this agent when I was a student at Penn, so it wasn't totally unknown to me, but he gave me more information. Bob told me that the mystery is that this agent which we're almost sure is a virus cannot be cultivated. We've failed to cultivate it in cell culture. It can be cultivated in embryonated chicken eggs, which was a fundamental tool for culturing viruses prior to the introduction of cell culture. And even to this day, most flu vaccines are produced in embryonated eggs because most but not all strains of flu viruses cannot grow in cell culture. That's a generality. So Bob said... told me that Monroe Eaton and he, Bob, have passaged this mysterious organism in embryonated chicken eggs and that's how they work with it. And what they learned was that this agent had an affinity for the trachea of the developing chick embryo and consequently if you made antibody to this mysterious organism, which you could easily do at that time, you could attach a fluorescent dye to the antibody and the antibody would stick to this mysterious organisms which itself is stuck to the trachea of the developing chick embryo and it would light up with this fluorescent light using the proper microscopic conditions of what's called 'fluorescent microscopy'. So you could actually see where it was on the lining of the trachea and that was an important way of knowing, a) whether you were growing it, b) the kind of pathology it was producing, etc.