‘It throws all sorts of light on nervous physiology, it kicks the theory of vision into a perfectly new shape.... Heaven knows how many thousand times. We’ll try all that after—— The thing is to try the stuff now.’

‘Try the stuff?’ I said, as we went along the passage.

‘Rather,’ said Gibberne, turning on me in his study. ‘There it is in that little green phial there! Unless you happen to be afraid?’

I am a careful man by nature, and only theoretically adventurous. I was afraid. But on the other hand, there is pride.

‘Well,’ I haggled. ‘You say you’ve tried it?’

‘I’ve tried it,’ he said, ‘and I don’t look hurt by it, do I? I don’t even look livery, and I feel——’

I sat down. ‘Give me the potion,’ I said. ‘If the worst comes to the worst it will save having my hair cut, and that, I think, is one of the most hateful duties of a civilised man. How do you take the mixture?’

‘With water,’ said Gibberne, whacking down a carafe.

He stood up in front of his desk and regarded me in his easy-chair; his manner was suddenly affected by a touch of the Harley Street specialist. ‘It’s rum stuff, you know,’ he said.

I made a gesture with my hand.