"Because I believe that you can throw some light upon this mysterious subject."
"Mysterious subject? Where is the mystery? The cause of Madame's death is clearly known!"
"You mean that she died of diphtheria. Yes, that is a fact. But how did she contract that disease? Is that clearly known? Can you throw any light upon that phase of the question?"
Leon controlled his agitation with great difficulty. He had thought, when urged on by that terrible temptation which he had resisted, that a death such as this would arouse no suspicion. Yet here, while the corpse was yet in the house, a detective was asking most horribly suggestive questions. Questions which had haunted him by day and by night, ever since that visit to the laboratory.
"I am not a physician," at length he murmured. "I am merely a student."
"Exactly! You are a student in the laboratory of Dr. Medjora. You can supply the information which I seek. Do you know whether, three days ago, there was a culture of the bacillus of diphtheria in the Doctor's laboratory?"
"Why do you ask? What do you suspect?"
Leon was utterly unnerved, and stammered in his utterance. He made a tremendous effort, in his endeavor to prevent his teeth from chattering, and barely succeeded. Indeed, his manner was so perturbed that for an instant Mr. Barnes suspected that he was guilty of some connection with Madame's death. A second later he guessed the truth, that Leon's suspicion's were identical with his own.
"What I think," said Mr. Barnes, "is not to the point. My question is a simple one. Will you reply to it?"
"Well, yes! We did have such a culture tube in the laboratory."