"You remember, I found his pupils contracted almost to a pin-point?" he asked.
"Yes. Was it morphine, as in the cases Doyle cited?"
Craig shook his head. "No, it wasn't morphine, either. I had to go at it with practically no other hint. However, in this case the elimination of drugs was comparatively easy. I simply began testing for all I could recall that had the effect of contracting the pupils of the eyes. There was one thing that helped very much. The contraction was so marked in this case that I started off by looking for the drug which occurred to me next after morphine. I don't claim any uncanny intelligence for it, either. That part of it was all just pure luck."
"Luck be hanged!" I exclaimed. "It's knowledge, preparedness. Would I ever have hit on it by luck?"
"Still, I was as much surprised to find it so soon as you are to hear it."
"I'll concede anything," I hastened. "I'm burning with curiosity. What was it?"
"Wilford died of physostigmine poisoning," he answered.
I suppose my face wrinkled with disappointment, for Craig laughed outright. "And—physostigmine—is what?" I inquired, quite willing to admit my ignorance if by that I might get ahead in understanding the mystery. "What does it do?"
"It's a drug used by oculists, just as they use atropin, but for the precisely opposite effect. Atropin dilates the pupils; physostigmine contracts them. Both are pre-eminent in their respective properties."
"Used by oculists!" I exclaimed, remembering suddenly that Honora Wilford's father, Honore Chappelle, had been an oculist.