“At the time when the war ended it was, as you can guess, a very closely guarded secret. Not more than four men knew anything about it. And then, the war over, and the necessity for its use no longer existing, the whole thing was rather pigeonholed. In fact it was only the day before yesterday, on the receipt of Gaunt’s request, that the matter was unearthed again. Naturally we imagined that it was still just as close a secret as ever. The events of last night prove that it cannot have been, unless my alternative theory should prove to be correct. And if that is so, Stockton, we are confronted with the unpleasant fact that someone is in possession of this very dangerous secret. Even in its Armistice stage the matter would be serious enough; but if Gaunt’s claims are correct, words are inadequate to express the dangers of the situation. Now, as anyone who is in the slightest degree in touch with the European pulse today knows, we are living on the edge of a volcano. And nothing must be done to start an eruption. Nothing, you understand. All personal feelings must go to the wall. In a moment or two I shall ask Sir John to say a few words, and from him you will realise that the first and lesser of the two points has evidently been rectified by Gaunt. What of the second and greater one? Until we know that, nothing must even be hinted at in the papers as to the nature of the issues at stake. And that brings me to my point. When you give your evidence at the inquest, Stockton, I want you to obliterate from your mind the conversation you had with Gaunt last night. The whole force of Scotland Yard is being employed to try and clear this thing up, and secrecy is essential. And we therefore rely entirely on your discretion and that of your friend, Mr. Sinclair.”
“You can certainly rely on him, sir,” I said. “But what am I to say, then? I must give some explanation?”
“Precisely: you must give some explanation,” he agreed. “But before I suggest to you what that explanation might be, I will ask Sir John to run over once more the conclusions he has arrived at.”
“They are quite obvious,” said the celebrated toxicologist. “As you may be aware, the vast majority of poisons must either be swallowed or injected to prove fatal. With the first class we are not concerned, but only with the second. In this second class the primary necessity is the introduction of the poison into a vein. You may have the bite of a snake, the use of a hypodermic syringe, or the prick of a poisoned dart—each of which causes a definite puncture in the skin through which the poison passes into a vein. And in each of those cases the puncture is caused mechanically—by the snake’s fang, or the dart, as the case may be.
“Now there is another tiny class of poisons—it is really a subdivision of the second class—of which, frankly, we know very little. Some expert toxicologists are even inclined to dismiss them as legendary. I’m not sure that I myself didn’t belong to their number until this morning. Evidence is in existence—but it is not reliable—of the use of these poisons by the Borgias, and by the Aztecs of Mexico. They were reputed to kill by mere external application, without the necessity of a puncture in the skin. They were supposed to generate some strange shattering force, which killed the victim by shock. Now that is absurd: no poison can kill unless it reacts point-blank on the heart. In other words, a puncture is necessary, and this class supplies its own punctures.
“You remember the policeman’s last words—‘The dog is burning hot.’ What he felt was a mass of small open blisters breaking out on his hand, through which the poison passed into his veins and up his arm to his heart. Had he touched the dog anywhere else nothing would have happened: as bad luck would have it he put his hand on the very spot where the poison had been applied to the dog.
“So much is clear. In all three cases that eruption of open blisters is there: in the dog above its shoulder, in the policeman on his hand, and in the case of the Australian on his right temple. And excepting in those places it is perfectly safe to touch the bodies.
“Now I was in that house at four o’clock this morning: the Inspector, very rightly, judged that time was an important factor and called me up. I took down with me several guinea-pigs, and I carried out a series of tests. I held a guinea-pig against the danger spot in each body, and the three guinea-pigs all died. I did the same an hour later. The one I put against the dog died: the one I put against the policeman’s hand died, but the one I put on the Australian’s forehead did not. It is possible that that means that the Australian was killed some time before the dog: on the other hand, it may merely prove that the dog’s long coat retained the poison more effectively. Finally, I used three more guinea-pigs at six o’clock, and nothing happened to any of them.
“My conclusions, therefore, are as follows: and, needless to say, they concern only the poison itself and not what actually happened last night. Mr. Gaunt has discovered a poison which, judging from the few tests I have carried out already, is unknown to science. It kills almost instantaneously when applied externally to the bare skin. Its effect lingers for some
