Kennedy apparently did not wish to encourage my quick deduction, for he paid no attention. "Yes," he repeated, thoughtfully, "it causes a contraction of the pupils more marked than that produced by any other drug I know. That was why I tried the test for it first—simply because it was at the top of the scale, so to speak."
Interested as I was in physostigmine, which, by the way, now came tripping off my tongue like the name of an old friend, I could not forget our first acquaintance with the case.
"But what about the atropin in the glass—and in the bottle?" I asked, hesitatingly.
"I did not say that I had cleared up the case," cautioned Craig. "It is still a mystery. Atropin has not only the opposite effect on the eye from physostigmine, but there is a further most unusual fact about the relationship of these two drugs. This is one of the few cases where we find drugs mutually antagonistic. And they are antagonistic to a marked degree in this instance, too."
He paused a moment and I tried to follow him, but was too bewildered to make an inch of progress. Here was a man killed, we knew, by a drug which Craig had recognized. Yet in the glass on his desk had been found unmistakable traces of another drug. Was it an elaborate camouflage? If so, it seemed to be utterly purposeless, for, even if Kennedy had not discovered the poison, the veriest tyro at the game must have done so comparatively soon. I gave it up. I could see no chance that the atropin might have been put in the glass either to point or to obscure suspicion. It was too clumsy and a brain clever enough to have conceived the whole thing would not have fallen into such an egregious error. It was too easy. But, if the obvious were rejected, what remained? By the grave look on Kennedy's face I was convinced that there was a depth of meaning to this apparent contradiction which even he himself had not fathomed yet.
"Atropin is an antidote to physostigmine," he continued. "Three and a half times the quantity almost infallibly counteracts the poisonous dose."
"But," I objected, "there was no trace of physostigmine in either glass, was there?"
"No," he replied, "the glasses are here. I got them from Doyle's office while you were away. Not a trace in either. In fact, one of the glasses is really free from belladonna traces. The physostigmine I discovered was all in the stomach contents of Wilford—and there is a great deal of it, too. When you come right down to the point, we've taken a step forward—that's all. There's a long way to go yet."
"But what of the physostigmine?" I queried. "How do you suppose it was given?"
He shook his head in doubt. "I made a close examination. There were no marks on the body such as if a needle had been used. Besides, my investigations showed that a needle need not have been used. There are peculiar starch grains in the stomach associated with the poison. I admit I still have no explanation of that."