In my absence Craig had set to work on a peculiar apparatus, as though he were distilling something from several of the cigarette stubs which he had been studying by means of the interferometer.

"Here's your confounded cat," I ejaculated, as I placed the unhappy feline in a basket and waited patiently until finally he seemed to be rewarded for his patient labours. It was well along toward morning when he obtained in a test-tube a few drops of a colourless, odourless liquid.

"My interferometer gave me a clue," he remarked, as he held the tube up with satisfaction. "Without the tell-tale line in the spectrum which I was able to discover by its use I might have been hunting yet for it. It is so rare that no one would ever have thought, offhand, I suppose, to look for it. But here it is, I'm sure, only I wanted to be able to test it."

"So you are not going to try it on yourself," I said sarcastically, referring to his last experiment with a poison. "This time you are going to make the cat the dog."

"The cat will be better to test it on than a human being," he replied, with a glance that made me wince, for, after his performance with the curare, I felt that once the scientific furore was on him I might be called upon to become an unwilling martyr to science.

It was with an air of relief, both for himself and my own peace and safety, that I saw him take the cat out of the basket and hold her in his arms, smoothing her fur gently, to quiet the feelings that I had severely ruffled.

Then with a dropper he sucked up a bit of the liquid from the test-tube. I watched him intently as he let a small drop fall into the eye of the cat.

The cat blinked a moment, and I bent over to observe it more closely.

"It won't hurt the cat," he explained, "and it may help us."

As I looked at the cat's eye it seemed to enlarge, even under the glare of a light, shining forth, as it were, like the proverbial cat's eye under a bed.

What did it mean?

Was there such a thing, I wondered hastily, as the drug of the evil eye?

"What have you found?" I queried.

"Something very much like the so-called 'weed of madness,' I think," he replied slowly.

"The weed of madness?" I repeated.

"Yes. It is similar to the Mexican toloache and the Hindu datura, which you must have heard about."

I had heard of these weird drugs, but they had always seemed to be so far away and to belong rather to the atmosphere of civilizations different from New York. Yet, I reflected, what was to prevent the appearance of anything in such a cosmopolitan city, especially in a case so unusual as that which had so far baffled even Kennedy's skill?

"You know the jimson weed—the Jamestown weed, as it is so often called?" he continued, explaining. "It grows almost everywhere in the world, but most thrivingly in the tropics. All the poisons that I have mentioned are related to it in some way, I believe."

"I've seen the thing in lots and fields," I replied, "but I never thought it was of much importance."

"Well," he resumed, "the jimson weed on the Pacific coast, in some parts of the Andes, has large white flowers which exhale a faint, repulsive odour. It is a harmless-looking plant, with its thick tangle of leaves, a coarse green growth, with trumpet-shaped flowers. But to one who knows its properties it is quite too dangerously convenient for safety."

"But what has that to do with the evil eye?" I asked.

"Nothing; but it has much to do with the cigarettes that Whitney is smoking," he went on positively. "Those cigarettes have been doped!"

"Doped?" I interrogated, in surprise. "With this weed of madness, as you call it?"

"No, it isn't toloache that was used," he corrected. "I think it must be some particularly virulent variety of the jimson weed that was used, though that same weed in Mexico is, I am sure, what there they call toloache. Perhaps its virulence in this case lies in the method of concentration in preparing it. For instance, the seeds of the stramonium, which is the same thing, contain a much higher percentage of poison than the leaves and flowers. Perhaps the seeds were used. I can't say. But, then, that isn't at all necessary. It is the fact of its use that concerns us most now."

He took a drop of the liquid which he had isolated and added a drop of nitric acid. Then he evaporated it by gentle heat and it left a residue slightly yellow.

Next he took from the shelf over his table a bottle marked "Alcoholic Solution—Potassium Hydrate." He opened it and let a drop fall on the place where the liquid had evaporated.

Instantly the residue became a beautiful purple, turning rapidly to violet, then to dark red, and, finally, it disappeared altogether.

"Stramonium, all right," he nodded, with satisfaction at the achievement of his night's labours. "That was known as Vitali's test. Yes, there was stramonium in those cigarettes—datura stramonium—perhaps a trace of hyoscyamine."

I tried to look wise, but all I could think of was that, whatever his science showed me now, my instinct had been enough to prompt me not to smoke those cigarettes, though, of course, only Kennedy's science could tell what it was that caused that instinctive aversion.

"They are all like atropine, mydriatic alkaloids," he proceeded, "so called from the effect they have on the eye. Why, one-one hundred thousandth of a grain will affect the eye of a cat. You saw how it acted on our subject. It is more active in that way than atropine. Better yet, you remember how Whitney's eyes looked, how Inez said her father stared, and how she feared for Lockwood?"

"I remember," I said, still not able to detach the evil-eye idea quite from my mind. "How about the Senora's eyes? What makes them so—well, effective?"

"Oh," Craig answered quickly, "her pupils were normal enough. Didn't you notice that? It was the difference in Whitney's and the others' that first suggested making some tests."

"What is the effect?" I asked, wondering whether it might have contributed to the cause of Mendoza's death.

"The concentrated poison which has been used in these cigarettes does not kill—at least not outright. It is worse than that. Slowly it accumulates in the system. It acts on the brain."

I was listening, spellbound, as he made his disclosure. No wonder, I thought, even a scientific criminal stood in awe of Craig.

"Of all the dangers to be met with in superstitious countries, these mydratic alkaloids are among the worst. They offer a chance for crimes of the most fiendish nature—worse than with the gun or the stiletto. They are worse because there is so little fear of detection. That crime is the production of insanity!"

Horrible though the idea, and repulsive, I could not doubt it in the face of Craig's investigations and what I had already seen with my own eyes. In fact, it was necessary for me only to recall the mild sensations I myself had experienced, in order to be convinced of the possible effect intended by the insidious poison contained in the many cigarettes which Whitney, for instance, had smoked.

"But don't you suppose they know it?" I wondered. "Can't they tell it?"

"I suppose they have gradually become accustomed to it," Craig ventured. "If you have ever smoked one particular brand of cigarette you must have noticed how the manufacturer can gradually substitute a cheaper grade of tobacco without any large number of his patrons knowing anything about it. I imagine it might have been done in some way like that."

"But you would think they'd feel the effect and attribute it to smoking."

"Perhaps they do feel the effect. But when it comes to tracing causes, some people are loath to admit that tobacco and liquor can be the root of the evil. No, some one is slipping these cigarettes in on them, perhaps substituting the doped brand for those that are ordered. If you will notice, both Whitney and Lockwood have cigarettes that are made especially for them. So had Mendoza. It is a circumstance which some one has turned to account, though how and by whom the substitution has been made I cannot say yet. I wish I had time to follow out this one line, to the exclusion of everything else. But I've got to keep my fingers on every rope at once, else the thing will pull away from me. It is enough for the present that we know what the poison is. I shall take up the tracing of the person who is administering it the moment I get a hint."

It was almost daylight before Craig and I left the laboratory after his discovery of the manner of the cigarette poisoning by stramonium. But that was the only way in which he was able to make progress—taking time for each separate point by main force.

I was thoroughly tired, though not so much so that my dreams were not haunted by a succession of baleful eyes peering at me from the darkness.

I slept late, but was awakened by a knocking on the door. As I rose to answer it I saw through the open door of Kennedy's room that he had been about early and must already be at the laboratory. How he did it I don't know. My own newspaper experience had made me considerable of a nighthawk. But I always paid for it by sleeping the next day. With Kennedy, when he was on a case, even five hours of sleep was more than he seemed able to stand.

"Hello, Jameson," greeted a voice, as I opened the door. "Is Kennedy in—oh, he hasn't come back yet?"

It was Lockwood, at first eager to see Craig, then naturally crestfallen because he saw that he was not there.

"Yes," I replied, rubbing my eyes. "He must be at the laboratory. If you'll wait a minute while I slip on my clothes, I'll walk over there with you."

While I completed my hasty toilet, Lockwood sat in our living room, gazing about with fascination at the collection of trophies of the chase of criminals.

"This is positively a terrifying array of material, Jameson," he declared, as at last I emerged. "Between what Kennedy has here and what he has stowed away in that laboratory of his, I wonder that any one dares be a crook."

I could not help eying him keenly. Could he have spoken so heartily if he had known what it was, damning to himself, that Kennedy had tucked away in the laboratory? If he knew, he must have been a splendid actor, one of those whom only the minute blood-pressure test of the sphygmograph could induce to give up a secret, and then only in spite of himself.

"It is wonderful," I agreed. "Are you ready?"

We left the apartment and walked along in the bracing morning air toward the campus and the Chemistry Building. Sure enough, as I had expected, Kennedy was in his laboratory.

As we entered he was verifying his experiments and checking over his results, carefully endeavouring to isolate any of the other closely related mydriatic alkaloids that might be contained in the noxious fumes of the poisoned tobacco.

Though Craig was already convinced of what was going on, I knew that he always considered it a matter of considerable medico-legal importance to be exact, for if the affair ever came to the stage of securing an indictment the charge could be sustained only by specific proof.

As we appeared in the door, however, he laid aside his work, and greeted us.

"I suppose Jameson has already told you that I called you up last night—and what I said?" began Lockwood.

Kennedy nodded. "It was something about Norton, wasn't it?"

Lockwood leaned over impressively and almost whispered: "Of course, you are in no position to know, but there are ugly rumours current down in Lima among the natives regarding that dagger."

Kennedy did not appear to be particularly impressed. "Is that so?" he said merely. "What are they?"

"Well," resumed Lockwood, "I wasn't in Lima at the time. I was up here. But they tell me that there was something crooked about the way that that dagger was got away from an Indian—a brother of Senora de Moche." "Yes," replied Kennedy, "I know something about it. He committed suicide. But what has that to do with Norton?"

Lockwood hesitated, then shrugged his shoulders. "I should think the inference was plain," he insinuated. Then, looking at Craig fixedly, as though to take his measure, he added, "We are not out of touch with what is going on down there, even if we are several thousand miles away."

I wondered whether he had any information more than we had already obtained by X-raying the letter to Whitney signed "Haggerty." If he had, it was not his purpose, evidently, yet to disclose it. I felt from his manner that he was not playing a trump-card, but was just feeling us out by this lead.

"There was some crooked business about that dagger down there as well as here," he pursued. "There are many interests connected with it. Don't you think that it would be worth while watching Norton?" he paused, then added: "We do—and we're going to do it."

"Thank you very much," returned Kennedy quietly. "Mr. Whitney has already told me he intended to do so."

Lockwood eyed us critically, as though not quite sure what to make of the cool manner in which Craig took it.

"I think if I were you," he said at length, "I'd keep a close watch on the de Moches, both of them, too."

"Exactly," agreed Craig, without showing undue interest.

Lockwood had risen. "Well," he snapped, "you may not think much of what I am telling you now. But just wait until OUR detectives begin to dig up facts." No sooner had he left than I turned to Craig. "What was that?" I asked. "A plant?"

"Perhaps," he returned, clearing up the materials which he had been using.

The telephone rang.

"Hello, Norton," I heard Craig answer. "What's that? You are shadowed by some one—you think it is by Whitney?"

I had been expecting something of the sort, and listened attentively, but it was impossible to gather the drift of the one-sided conversation.

As Kennedy hung up the receiver I remarked, "So it was not a bluff, after all."

"I think my plan is working," he remarked thoughtfully. "You heard what he said? He guesses right the first time, that it is Whitney. The last thing he said was, 'I'll get even! I'll take some action!' and then he rang off. I think we'll hear something soon."

Instead of going out, Kennedy pulled out the several unsigned letters we had collected, and began the laborious process of studying the printing, analyzing it, in the hope that he might discover some new clue.