“I will now cut one of these pills in two,” said Holmes, and drawing his penknife he suited the action to the word. “One half we return into the box for future purposes. The other half I will place in this wine glass, in which is a teaspoonful of water. You perceive that our friend, the Doctor, is right, and that it readily dissolves.”

“This may be very interesting,” said Lestrade, in the injured tone of one who suspects that he is being laughed at, “I cannot see, however, what it has to do with the death of Mr. Joseph Stangerson.”

“Patience, my friend, patience! You will find in time that it has everything to do with it. I shall now add a little milk to make the mixture palatable, and on presenting it to the dog we find that he laps it up readily enough.”

As he spoke he turned the contents of the wine glass into a saucer and placed it in front of the terrier, who speedily licked it dry. Sherlock Holmes’ earnest demeanour had so far convinced us that we all sat in silence, watching the animal intently, and expecting some startling effect. None such appeared, however. The dog continued to lie stretched upon the cushion, breathing in a laboured way, but apparently neither the better nor the worse for its draught.

Holmes had taken out his watch, and as minute followed minute without result, an expression of the utmost chagrin and disappointment appeared upon his features. He gnawed his lip, drummed his fingers upon the table, and showed every other symptom of acute impatience. So great was his emotion, that I felt sincerely sorry for him, while the two detectives smiled derisively, by no means displeased at this check which he had met.

“It can’t be a coincidence,” he cried, at last springing from his chair and pacing wildly up and down the room; “it is impossible that it should be a mere coincidence. The very pills which I suspected in the case of Drebber are actually found after the death of Stangerson. And yet they are inert. What can it mean? Surely my whole chain of reasoning cannot have been false. It is impossible! And yet this wretched dog is none the worse. Ah, I have it! I have it!” With a perfect shriek of delight he rushed to the box, cut the other pill in two, dissolved it, added milk, and presented it to the terrier. The unfortunate creature’s tongue seemed hardly to have been moistened in it before it gave a convulsive shiver in every limb, and lay as rigid and lifeless as if it had been struck by lightning.