“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.
Lowenstein! The name brought back to me the memory of some snippet from a newspaper which spoke of an obscure scientist who was striving in some unknown way for the secret of rejuvenescence and the elixir of life. Lowenstein of Prague! Lowenstein with the wondrous strength-giving serum, tabooed by the profession because he refused to reveal its source. In a few words I said what I remembered. Bennett had taken a manual of Zoology from the shelves. ‘‘‘Langur,’” he read, “‘the great black-faced monkey of the Himalayan slopes, biggest and most human of climbing monkeys.’ Many details are added. Well, thanks to you, Mr. Holmes, it is very clear that we have traced the evil to its source.”
