And then in a moment it happened! It was not the chain that broke, but it was the collar that slipped, for it had been made for a thick-necked Newfoundland. We heard the rattle of falling metal, and the next instant dog and man were rolling on the ground together, the one roaring in rage, the other screaming in a strange shrill falsetto of terror. It was a very narrow thing for the professor’s life. The savage creature had him fairly by the throat, its fangs had bitten deep, and he was senseless before we could reach them and drag the two apart. It might have been a dangerous task for us, but Bennett’s voice and presence brought the great wolfhound instantly to reason. The uproar had brought the sleepy and astonished coachman from his room above the stables. “I’m not surprised,” said he, shaking his head. “I’ve seen him at it before. I knew the dog would get him sooner or later.”

The hound was secured, and together we carried the professor up to his room, where Bennett, who had a medical degree, helped me to dress his torn throat. The sharp teeth had passed dangerously near the carotid artery, and the haemorrhage was serious. In half an hour the danger was past, I had given the patient an injection of morphia, and he had sunk into deep sleep. Then, and only then, were we able to look at each other and to take stock of the situation.

“I think a first-class surgeon should see him,” said I.

“For God’s sake, no!” cried Bennett. “At present the scandal is confined to our own household. It is safe with us. If it gets beyond these walls it will never stop. Consider his position at the university, his European reputation, the feelings of his daughter.”

“Quite so,” said Holmes. “I think it may be quite possible to keep the matter to ourselves, and also to prevent its recurrence now that we have a free hand. The key from the watch-chain, Mr. Bennett. Macphail will guard the patient and let us know if there is any change. Let us see what we can find in the professor’s mysterious box.”

There was not much, but there was enough - an empty phial, another nearly full, a hypodermic syringe, several letters in a crabbed, foreign hand. The marks on the envelopes showed that they were those which had disturbed the routine of the secretary, and each was dated from the Commercial Road and signed “A. Dorak.” They were mere invoices to say that a fresh bottle was being sent to Professor Presbury, or receipt to acknowledge money. There was one other envelope, however, in a more educated hand and bearing the Austrian stamp with the postmark of Prague. “Here we have our material!” cried Holmes as he tore out the enclosure.

HONOURED COLLEAGUE [it ran]:

Since your esteemed visit I have thought much of your case, and though in your circumstances there are some special reasons for the treatment, I would none the less enjoin caution, as my results have shown that it is not without danger of a kind.

It is possible that the serum of anthropoid would have been better. I have, as I explained to you, used black-faced langur because a specimen was accessible. Langur is, of course, a crawler and climber, while anthropoid walks erect and is in all ways nearer.

I beg you to take every possible precaution that there be no premature revelation of the process. I have one other client in England, and Dorak is my agent for both.

Weekly reports will oblige.

Yours with high esteem,

H. LOWENSTEIN.