As I say, any interest I could feel was kindled by Franklin's conversation with Poirot.

He said:

"You know, Poirot, the stuffs really more up your street than mine. It's the ordeal bean - supposed to prove innocence or guilt. These West African tribes believe it implicitly - or did do so - they're getting sophisticated nowadays. They'll solemnly chew it up quite confident that it will kill them if they're guilty and not harm them if they're innocent."

"And so, alas, they die?"

"No, they don't all die. That's what has always been overlooked up to now. There's a lot behind the whole thing - a medicine man ramp, I rather fancy. There are two distinct species of this bean - only they look so much alike that you can hardly spot the difference. But there is a difference. They both contain physostigmine and geneserine and the rest of it, but in the second species you can isolate, or I think I can, yet another alkaloid - and the action of that alkaloid neutralizes the effect of the others. What's more, that second species is regularly eaten by a kind of inner ring in a secret ritual - and the people who eat it never go down with Jordanitis. This third substance has a remarkable effect on the muscular system - without deleterious effects. It's damned interesting. Unfortunately the pure alkaloid is very unstable. Still, I'm getting results. But what's wanted is a lot more research out there on the spot. It's work that ought to be done! Yes, by heck, it is ... I'd sell my soul to - "

He broke off abruptly. The grin came again.

"Forgive the shop. I get too het up over these things!"

"As you say," said Poirot placidly, "it would certainly make my profession much easier if I could test guilt and innocence so easily. Ah, if there were a substance that could do what is claimed for the Calabar bean!"

Franklin said:

"Ah, but your troubles wouldn't end there! After all, what is guilt or innocence?"

"I shouldn't think there could be any doubt about that," I remarked. He turned to me.

"What is evil? What is good? Ideas on them vary from century to century. What you would be testing would probably be a sense of guilt or a sense of innocence. In fact no value as a test at all."

"I don't see how you make that out."

"My dear fellow, suppose a man thinks he has a divine right to kill a dictator or a moneylender or a pimp or whatever arouses his moral indignation. He commits what you consider a guilty deed - but what he considers is an innocent one? What is your poor ordeal bean to do about it?"

"Surely," I said, "there must always be a feeling of guilt with murder?"

"Lots of people I'd like to kill," said Dr. Franklin cheerfully. "Don't believe my conscience would keep me awake at night afterwards. It's an idea of mine, you know, that about eighty per cent of the human race ought to be eliminated. We'd get on much better without them."