“If the cycle of nine days holds good then we shall have the professor at his worst to-night,” said Holmes. “The fact that these strange symptoms began after his visit to Prague, that he is in secret correspondence with a Bohemian dealer in London, who presumably represents someone in Prague, and that he received a packet from him this very day, all point in one direction. What he takes and why he takes it are still beyond our ken, but that it emanates in some way from Prague is clear enough. He takes it under definite directions which regulate this ninth-day system, which was the first point which attracted my attention. But his symptoms are most remarkable. Did you observe his knuckles?”

I had to confess that I did not.

“Thick and horny in a way which is quite new in my experience. Always look at the hands first, Watson. Then cuffs, trouser-knees, and boots. Very curious knuckles which can only be explained by the mode of progression observed by- -” Holmes paused and suddenly clapped his hand to his forehead. “Oh, Watson, Watson, what a fool I have been! It seems incredible, and yet it must be true. All points in one direction. How could I miss seeing the connection of ideas? Those knuckles - how could I have passed those knuckles? And the dog! And the ivy! It’s surely time that I disappeared into that little farm of my dreams. Look out, Watson! Here he is! We shall have the chance of seeing for ourselves.”

The hall door had slowly opened, and against the lamplit background we saw the tall figure of Professor Presbury. He was clad in his dressing-gown. As he stood outlined in the doorway he was erect but leaning forward with dangling arms, as when we saw him last.

Now he stepped forward into the drive, and an extraordinary change came over him. He sank down into a crouching position and moved along upon his hands and feet, skipping every now and then as if he were overflowing with energy and vitality. He moved along the face of the house and then round the corner. As he disappeared Bennett slipped through the hall door and softly followed him.

“Come, Watson, come!” cried Holmes, and we stole as softly as we could through the bushes until we had gained a spot whence we could see the other side of the house, which was bathed in the light of the half-moon. The professor was clearly visible crouching at the foot of the ivy-covered wall. As we watched him he suddenly began with incredible agility to ascend it. From branch to branch he sprang, sure of foot and firm of grasp, climbing apparently in mere joy at his own powers, with no definite object in view. With his dressing-gown flapping on each side of him, he looked like some huge bat glued against the side of his own house, a great square dark patch upon the moonlit wall. Presently he tired of this amusement, and, dropping from branch to branch, he squatted down into the old attitude and moved towards the stables, creeping along in the same strange way as before. The wolfhound was out now, barking furiously, and more excited than ever when it actually caught sight of its master. It was straining on its chain and quivering with eagerness and rage. The professor squatted down very deliberately just out of reach of the hound and began to provoke it in every possible way. He took handfuls of pebbles from the drive and threw them in the dog’s face, prodded him with a stick which he had picked up, flicked his hands about only a few inches from the gaping mouth, and endeavoured in every way to increase the animal’s fury, which was already beyond all control. In all our adventures I do not know that I have ever seen a more strange sight than this impassive and still dignified figure crouching frog-like upon the ground and goading to a wilder exhibition of passion the maddened hound, which ramped and raged in front of him, by all manner of ingenious and calculated cruelty.