The principle that I tried to establish was really that it was not necessary to run the risk of infection, which would have been the case if one were to try to develop an attenuated or weakened polio virus vaccine. And so it seemed to me the safer and more certain way to proceed. That if we could inactivate the virus that we could move on to a vaccine very quickly. Whereas, if you were dealing with weakened virus, you would have to demonstrate its safety eventually. So that was the reasoning and there was a principle that was involved. You might say a scientific principle, a fundamental principle: choosing and preferring that which — the safety which you could control, and the quantities which you could use. So that this is, in a way, a more scientific approach. Trying to work like nature, instead of imitating nature.