“I took it for granted that Prouty and the Medical Examiner had done the preliminaries very well,” began Dr. Jones, crossing his bony knees. “They generally do. And so, before doing anything else, I analyzed for the obscure poisons. Obscure, that is to say, from the standpoint of the criminal user. To show you how minutely I searched—I even thought of that favorite stand-by of our friends the fiction-writers: _curare_, the South American toxin which makes the grade in four out of five detective stories. But even that sadly abused member of the toxic family disappointed me....” Ellery leaned back and laughed. “If you’re referring in a mildly satirical way to my profession, Dr. Jones, let me inform you that I have never used _curare_ in any of my novels.” The toxicologist’s eyes twinkled. “So you’re one of them, too, eh? Queen, old man,” he added dolorously, turning to the Inspector, who was thoughtfully chewing on a piece of French pastry, “allow me to offer you my condolences.... At any rate, gentlemen, let me explain that in the case of rare poisons we can generally come to a definite conclusion without much trouble—that is, rare poisons that are in the pharmacopœia. Of course, there are any number of rare poisons of which we have no knowledge whatever—Eastern drugs particularly. “Well, to make a long story short, I found myself faced with the unpleasant conclusion that I was up a tree.” Dr. Jones chuckled in reminiscence. “It wasn’t a pleasant conclusion. The poison I analyzed had certain properties which were vaguely familiar, as Prouty has said, and others which didn’t jibe at all. I spent most of yesterday evening mulling over my retorts and test-tubes, and late last night I suddenly got the answer.” Ellery and Queen sat up straight and Dr. Prouty relaxed in his chair with a sigh, reaching for a second cup of coffee. The toxicologist uncrossed his legs, his voice booming more terrifyingly than ever. “The poison that killed your victim, Inspector, is known as tetra ethyl lead!” To a scientist this announcement, in Dr. Jones’ profoundest tones, might have carried a dramatic quality. To the Inspector it meant less than nothing. As for Ellery, he murmured, “Sounds like a mythological monster to me!” Dr. Jones went on, smiling. “So it hasn’t impressed you much, eh? But let me tell you a little about tetra ethyl lead. It is almost colorless—to be more exact, it resembles chloroform in physical appearance. Point number one. Point number two—it has an odor—faint, to be sure—but distinctly like that of ether. Point number three—it is fearfully potent. So potent—but let me illustrate just what this devilishly powerful chemical substance will do to living tissue.” By this time the toxicologist had gained the entire attention of his audience.