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I had scarcely had time to assure Kennedy of the success of my mission, when we were surprised to see the door open and Seabury himself appear.

His face was actually haggard. Whether or not he had believed the hastily concocted story of Kennedy at the Vanderveer, his mind had not ceased to work on the other fears that had prompted his coming to us in the first place.

“I’ve been trying to locate you all over,” greeted Craig.

Seabury heaved a sigh and passed his hand, with its familiar motion, over his forehead. “I thought perhaps you might be able to find out something from this stuff,” he answered, unwrapping a package which he was carrying. “Some samples of the food I’ve been getting. If you don’t find anything in this, I’ve others I want tested.”

As I looked at the man’s drawn face, I wondered whether in fact there might be something in his fears. On the surface, the thing did indeed seem to place Agatha Seabury in a bad light. At the sight of the key in Sherburne’s possession I had grasped at the straw that he might have conceived some diabolical plan to get rid of Seabury for purposes of his own. But then, I reasoned, would he have been so free in showing the key if he had realized that it might cast suspicion on himself? I was forced to ask myself again whether she might, in her hysterical fear of exposure by the adroit blackmailer, have really attempted to poison her husband.

It was a desperate situation. But Kennedy was apparently ready to meet it, though he seemed to take no great interest in the food samples Seabury had just brought.

Instead he seemed to rely wholly on the tests he had already begun with the peculiar tissue I had seen him boiling and the blood serum derived from Seabury himself.

Without a word he took three tubes from the incubator, in which I had seen him place them some time before, and, as they stood in a rack, indicated them lightly with his finger.

“I think I can clear part of this mystery up immediately,” he began, speaking more to himself than to Seabury and myself. “Here I have a tested dialyzer in which has been placed a half cubic centimeter of pure clear serum. Here is another dialyzer with the same amount of serum, but no tissue, such as Mr. Jameson has seen me place in this first one. Here is still another with the tissue in distilled water, but no blood serum. I have placed all the dialyzers in tubes of distilled water and all are covered with a substance known as toluol and corked to keep them from contamination.”

Kennedy held up before us the three tubes and Seabury gazed on them with a sort of fascination, scarcely believing that in them in some way might be contained the verdict on the momentous problem that troubled his mind and might perhaps mean life or death to him.

Carefully Kennedy took from each tube a few cubic centimeters of the dialyzate and into each he poured a little liquid from a tiny vial which I noticed was labelled “Ninhydrin.”

“This,” he explained as he set down the vial, “is a substance which gives a colorless solution with water, but when mixed with albumins, peptones, or amino-acids becomes violet on boiling. Tube number three must remain colorless. Number two may be violet. Number one may approximate number two or be more deeply colored. If one and two are about the same I call my test negative. But if one is more deeply colored than two, then it is positive. The other tube is the control.”

Impatiently we waited as the three tubes simmered over the heat. What would they show? Seabury’s eyes were glued on them, his hand trembling in the presence of some unknown danger.

Slowly the liquid in the second tube turned to violet. But more rapidly and more deeply appeared the violet in number one. The test was positive.