None of us said much until, half an hour later, in the department laboratory, Leslie began to recapitulate what he had already done in the case.

"You asked whether I had examined the food," he remarked, pausing in a corner before several cages in which were a number of pigeons, separated and carefully tagged. With a wave of his hand at one group of cages he continued: "These fellows I have been feeding exclusively on samples of the various foods which I took from the Wardlaw family when I first went up there. Here, too, are charts showing what I have observed up to date. Over there are the 'controls'--pigeons from the same group which have been fed regularly on the usual diet so that I can check my tests."

Kennedy fell to examining the pigeons carefully as well as the charts and records of feeding and results. None of the birds fed on what had been taken from the apartment looked well, though some were worse than others.

"I want you to observe this fellow," pointed out Leslie at last, singling out one cage. The pigeon in it was a pathetic figure. His eyes seemed dull and glazed. He paid little or no attention to us; even his food and water did not seem to interest him. Instead of strutting about, he seemed to be positively wabbly on his feet. Kennedy examined this one longer and more carefully than any of the rest.

"There are certainly all the symptoms of beriberi, or rather, polyneuritis, in pigeons, with that bird," admitted Craig, finally, looking up at Leslie.

The commissioner seemed to be gratified. "You know," he remarked, "beriberi itself is a common disease in the Orient. There has been a good deal of study of it and the cause is now known to be the lack of something in the food, which in the Orient is mostly rice. Polishing the rice, which removes part of the outer coat, also takes away something that is necessary for life, which scientists now call 'vitamines.'"

"I may take some of these samples to study myself?" interrupted Kennedy, as though the story of vitamines was an old one to him.

"By all means," agreed Leslie.

Craig selected what he wanted, keeping each separate and marked, and excused himself, saying that he had some investigations of his own that he wished to make and would let Leslie know the result as soon as he discovered anything.

Kennedy did not go back directly to the laboratory, however. Instead, he went up-town and, to my surprise, stopped at one of the large breweries. What it was that he was after I could not imagine, but, after a conference with the manager, he obtained several quarts of brewer's yeast, which he had sent directly down to the laboratory.

Impatient though I was at this seeming neglect of the princ.i.p.al figures in the case, I knew, nevertheless, that Kennedy had already schemed out his campaign and that whatever it was he had in mind was of first importance.

Back at last in his own laboratory, Craig set to work on the brewer's yeast, deriving something from it by the plentiful use of a liquid labeled "Lloyd's reagent," a solution of hydrous aluminum silicate.

After working for some time, I saw that he had obtained a solid which he pressed into the form of little whitish tablets. He had by no means finished, but, noticing my impatience, he placed the three or four tablets in a little box and handed them to me.

"You might take these over to Leslie in the department laboratory, Walter," he directed. "Tell him to feed them to that wabbly-looking pigeon over there--and let me know the moment he observes any effect."

Glad of the chance to occupy myself, I hastened on the errand, and even presided over the first feeding of the bird.

When I returned I found that Kennedy had finished his work with the brewer's yeast and was now devoting himself to the study of the various samples of food which he had obtained from Leslie.

He was just finishing a test of the baking-powder when I entered, and his face showed plainly that he was puzzled by something that he had discovered.

"What is it?" I asked. "Have you found out anything?"

"This seems to be almost plain sodium carbonate," he replied, mechanically.

"And that indicates?" I prompted.

"Perhaps nothing, in itself," he went on, less abstractedly. "But the use of sodium carbonate and other things which I have discovered in other samples disengages carbon dioxide at the temperature of baking and cooking. If you'll look in that public-health report on my desk you'll see how the latest investigations have shown that bicarbonate of soda and a whole list of other things which liberate carbon dioxide destroy the vitamines Leslie was talking about. In other words, taken altogether I should almost say there was evidence that a concerted effort was being made to affect the food--a result a.n.a.logous to that of using polished rice as a staple diet--and producing beriberi, or, perhaps more accurately, polyneuritis. I can be sure of nothing yet, but--it's worth following up."

"Then you think Kato--"

"Not too fast," cautioned Craig. "Remember, others had access to the kitchen, too."

In spite of his hesitancy, I could think only of the two paragraphs we had read in Mrs. Wardlaw's will, and especially of the last. Might not Kato have been forced or enticed into a scheme that promised a safe return and practically no chance of discovery? What gruesome mystery had been unveiled by the anonymous letter which had first excited our curiosity?

It was late in the afternoon that Commissioner Leslie called us up, much excited, to inform us that the drooping pigeon was already pecking at food and beginning to show some interest in life. Kennedy seemed greatly gratified as he hung up the receiver.

"Almost dinner-time," he commented, with a glance at his watch. "I think we'll make another hurried visit to the Wardlaw apartment."

We had no trouble getting in, although as outsiders we were more tolerated than welcome. Our excuse was that Kennedy had some more questions which we wished to ask Miss Langdale.

While we waited for her we sat, not in the study, but in the parlor.

The folding-doors into the dining-room were closed, but across the hall we could tell by the sound when Kato was in the kitchen and when he crossed the hall.

Once I heard him in the dining-room. Before I knew it Kennedy had hastily tiptoed across the hall and into the kitchen. He was gone only a couple of minutes, but it was long enough to place in the food that was being prepared, and in some unprepared, either the tablets he had made or a powder he had derived from them crushed up. When he returned I saw from his manner that the real purpose of the visit had been accomplished, although when Miss Langdale appeared he went through the form of questioning her, mostly on Mrs. Marbury's sickness and death.

He did not learn anything that appeared to be important, but at least he covered up the reason for his visit. Outside the apartment, Kennedy paused a moment. "There's nothing to do now but await developments," he meditated. "Meanwhile, there is no use for us to double up our time together. I have decided to watch Kato to-night. Suppose you shadow Doctor Aitken. Perhaps we may get a line on something that way."

The plan seemed admirable to me. In fact, I had been longing for some action of the sort all the afternoon, while Kennedy had been engaged in the studies which he evidently deemed more important.

Accordingly, after dinner, we separated, Kennedy going back to the Forum Apartments to wait until Kato left for the night, while I walked farther up the Drive to the address given in the directory as that of Doctor Aitken.

It happened to be the time when the doctor had his office hours for patients, so that I was sure at least that he was at home when I took my station just down the street, carefully scrutinizing every one who entered and left his house.

Nothing happened, however, until the end of the hour during which he received office calls. As I glanced down the street I was glad that I had taken an inconspicuous post, for I could see Miss Langdale approaching. She was not in her nurse's uniform, but seemed to be off duty for an hour or two, and I must confess she was a striking figure, even in that neighborhood which was noted for its pretty and daintily gowned girls. Almost before I knew it she had entered the English-bas.e.m.e.nt entrance of Doctor Aitken's.

I thought rapidly. What could be the purpose of her visit? Above all, how was I, on the outside, to find out? I walked down past the house.

But that did no good. In a quandary, I stopped. Hesitation would get me nothing. Suddenly an idea flashed through my mind. I turned in and rang the bell.

"It's past the doctor's office hours," informed a servant who opened the door. "He sees no one after hours."

"But," I lied, "I have an appointment. Don't disturb him. I can wait."

The waiting-room was empty, I had seen, and I was determined to get in at any cost. Reluctantly the servant admitted me.

For several moments I sat quietly alone, fearful that the doctor might open the double doors of his office and discover me. But nothing happened and I grew bolder. Carefully I tiptoed to the door. It was of solid oak and practically impervious to sound. The doors fitted closely, too. Still, by applying my ear, I could make out the sound of voices on the other side. I strained my ears both to catch a word now and then and to be sure that I might hear the approach of anybody outside.

Was Aitken suspiciously interested in the pretty nurse--or was she suspiciously interested in him?

Suddenly their voices became a trifle more distinct. "Then you think Doctor Wardlaw has it, too?" I heard her ask. I did not catch the exact reply, but it was in the affirmative.

They were approaching the door. In a moment it would be opened. I waited to hear no more, but seized my hat and dashed for the entrance from the street just in time to escape observation. Miss Langdale came out shortly, the doctor accompanying her to the door, and I followed her back to the Forum.

What I had heard only added to the puzzle. Why her anxiety to know whether Wardlaw himself was affected? Why Aitken's solicitude in a.s.serting that he was? Were they working together, or were they really opposed? Which might be using the other?

My queries still unanswered, I returned to Aitken's and waited about some time, but nothing happened, and finally I went on to our own apartment.

It was very late when Craig came in, but I was still awake and waiting for him. Before I could ask him a question he was drawing from me what I had observed, listening attentively. Evidently he considered it of great importance, though no remark of his betrayed what interpretation he put on the episode.

"Have you found anything?" I managed to ask, finally.

"Yes, indeed," he nodded, thoughtfully. "I shadowed Kato from the Forum. It must have been before Miss Langdale came out that he left. He lives down-town in a tenement-house. There's something queer about that j.a.p."

"I think there is," I agreed. "I don't like his looks."

"But it wasn't he who interested me so much to-night," Craig went on, ignoring my remark, "as a woman."