“What do you suspect was the cause of that sweetish odour?” asked Kennedy.

The doctor hesitated.  “Mind, it is only a suspicion.  Cyanide of potassium or cyanogen gas; either would give such an odour.”

“Your treatment would have been just the same had you been certain?”

“Practically the same, the Rockefeller treatment.”

“Could it have been suicide” asked Andrews.

“There was no motive for it, I believe,” replied the doctor.

“But was there any such poison in the Morowitch house?”

“I know that they were much interested in photography.  Cyanide of potassium is used in certain processes in photography.”

“Who was interested in photography, Mr. or Mrs. Morowitch?”

“Both of them.”

“Was Mrs. Morowitch?”

“Both of them,” repeated the doctor hastily.  It was evident how Andrews’s questions were tending, and it was also evident that the doctor did not wish to commit himself or even to be misunderstood.

Kennedy had sat silently for some minutes, turning the thing over in his mind.  Apparently disregarding Andrews entirely, he now asked, “Doctor, supposing it had been cyanogen gas which caused the congestion of the lungs, and supposing it had not been inhaled in quantities large enough to kill outright, do you nevertheless feel that Mr. Morowitch was in a weak enough condition to die as a result of the congestion produced by the gas after the traces of the cyanogen had been perhaps thrown off?”

“That is precisely the impression which I wished to convey.”

“Might I ask whether in his semiconscious state he said anything that might at all serve as a clue?”

“He talked ramblingly, incoherently.  As near as I can remember it, he seemed to believe himself to have become a millionaire, a billionaire.  He talked of diamonds, diamonds, diamonds.  He seemed to be picking them up, running his fingers through them, and once I remember he seemed to want to send for Mr. Kahan and tell him something.  ‘I can make them, Kahan,’ he said, ’the finest, the largest, the whitest—­I can make them.’”

Kennedy was all attention as Dr. Thornton added this new evidence.

“You know,” concluded the doctor, “that in cyanogen poisoning there might be hallucinations of the wildest kind.  But then, too, in the delirium of pneumonia it might be the same.”

I could see by the way Kennedy acted that for the first time a ray of light had dawned upon him in tracing out the case.  As we rose to go, the doctor shook hands with us.  His last words were said with an air of great relief, “Gentlemen, I have eased my conscience considerably.”

As we parted for the night Kennedy faced Andrews.  “You recall that you promised me one thing when I took up this case?” he asked.

Andrews nodded.