longer. The old lady had to die—before Oppenheimer arrived. And half an hour later Ada took the morphine. She feared to give Mrs. Greene the strychnine at once lest it appear suspicious. . . ."
"That's where those books on poisons come in, isn't it, Mr. Vance?" interjected Heath. "When Ada had decided to use poison on some of the family, she got all the dope she needed on the subject outa the library."
"Precisely. She herself took just enough morphine to render her unconscious—probably about two grains. And to make sure she would get immediate assistance she devised the simple trick of having Sibella's dog appear to give the alarm. Incidentally, this trick cast suspicion on Sibella. After Ada had swallowed the morphine, she merely waited until she began to feel drowsy, pulled the bell-cord, caught the tassel in the dog's teeth, and lay back. She counterfeited a good deal of her illness; but Drumm couldn't have detected her malingering even if he had been as great a doctor as he wanted us to believe; for the symptoms for all doses of morphine taken by mouth are practically the same during the first half-hour. And, once she was on her feet, she had only to watch for an opportunity of giving the strychnine to Mrs. Greene. . . ."
"It all seems too cold-blooded to be real," murmured Markham.
"And yet there has been any number of precedents for Ada's actions. Do you recall the mass murders of those three nurses, Madame Jegado, Frau Zwanzigger, and Vrouw Van der Linden? And there was Mrs. Belle Gunness, the female Bluebeard; and Ame-
