“Plain enough—­my meaning,” replied Bryce, smiling.  “To finish anybody with that stuff is easy enough—­but no poison is more easily detected.  It’s an amateurish way of poisoning anybody—­unless you can do it in such a fashion that no suspicion can attach you to.  And in this case it’s here —­whoever administered that poison to Collishaw must have been certain—­absolutely certain, mind you!—­that it was impossible for any one to find out that he’d done so.  Therefore, I say what I said—­the man must be damned clever.  Otherwise, he’d be found out pretty quick.  And all that puzzles me is—­how was it administered?”

“How much would kill anybody—­pretty quick?” asked Mitchington.

“How much?  One drop would cause instantaneous death!” answered Bryce.  “Cause paralysis of the heart, there and then, instantly!”

Mitchington remained silent awhile, looking meditatively at Bryce.  Then he turned to a locked drawer, produced a key, and took something out of the drawer—­a small object, wrapped in paper.

“I’m telling you a good deal, doctor,” he said.  “But as you know so much already, I’ll tell you a bit more.  Look at this!”

He opened his hand and showed Bryce a small cardboard pill-box, across the face of which a few words were written —­One after meals—­Mr. Collishaw.

“Whose handwriting’s that?” demanded Mitchington.

Bryce looked closer, and started.

“Ransford’s!” he muttered.  “Ransford—­of course!”

“That box was in Collishaw’s waistcoat pocket,” said Mitchington.  “There are pills inside it, now.  See!” He took off the lid of the box and revealed four sugar-coated pills.  “It wouldn’t hold more than six, this,” he observed.

Bryce extracted a pill and put his nose to it, after scratching a little of the sugar coating away.

“Mere digestive pills,” he announced.

“Could—­it!—­have been given in one of these?” asked Mitchington.

“Possible,” replied Bryce.  He stood thinking for a moment.  “Have you shown those things to Coates and Everest?” he asked at last.

“Not yet,” replied Mitchington.  “I wanted to find out, first, if Ransford gave this box to Collishaw, and when.  I’m going to Collishaw’s house presently—­I’ve certain inquiries to make.  His widow’ll know about these pills.”

“You’re suspecting Ransford,” said Bryce.  “That’s certain!”

Mitchington carefully put away the pill-box and relocked the drawer.

“I’ve got some decidedly uncomfortable ideas—­which I’d much rather not have—­about Dr. Ransford,” he said.  “When one thing seems to fit into another, what is one to think.  If I were certain that that rumour which spread, about Collishaw’s knowledge of something—­you know, had got to Ransford’s ears —­why, I should say it looked very much as if Ransford wanted to stop Collishaw’s tongue for good before it could say more —­and next time, perhaps, something definite.  If men once begin to hint that they know something, they don’t stop at hinting.  Collishaw might have spoken plainly before long—­to us!”