When I tell my own story I have no such aid. And yet I will give my process of thought even as I gave it to my small audience, which included Godfrey’s mother in the study of Colonel Emsworth.
“That process,” said I, “starts upon the supposition that when you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth. It may well be that several explanations remain, in which case one tries test after test until one or other of them has a convincing amount of support. We will now apply this principle to the case in point. As it was first presented to me, there were three possible explanations of the seclusion or incarceration of this gentleman in an outhouse of his father’s mansion. There was the explanation that he was in hiding for a crime, or that he was mad and that they wished to avoid an asylum, or that he had some disease which caused his segregation. I could think of no other adequate solutions. These, then, had to be sifted and balanced against each other.
“The criminal solution would not bear inspection. No unsolved crime had been reported from that district. I was sure of that. If it were some crime not yet discovered, then clearly it would be to the interest of the family to get rid of the delinquent and send him abroad rather than keep him concealed at home. I could see no explanation for such a line of conduct.
“Insanity was more plausible. The presence of the second person in the outhouse suggested a keeper. The fact that he locked the door when he came out strengthened the supposition and gave the idea of constraint. On the other hand, this constraint could not be severe or the young man could not have got loose and come down to have a look at his friend. You will remember, Mr. Dodd, that I felt round for points, asking you, for example, about the paper which Mr. Kent was reading. Had it been the Lancet or the British Medical Journal it would have helped me. It is not illegal, however, to keep a lunatic upon private premises so long as there is a qualified person in attendance and that the authorities have been duly notified. Why, then, all this desperate desire for secrecy? Once again I could not get the theory to fit the facts.
“There remained the third possibility, into which, rare and unlikely as it was, everything seemed to fit. Leprosy is not uncommon in South Africa. By some extraordinary chance this youth might have contracted it. His people would be placed in a very dreadful position, since they would desire to save him from segregation. Great secrecy would be needed to prevent rumours from getting about and subsequent interference by the authorities. A devoted medical man, if sufficiently paid, would easily be found to take charge of the sufferer. There would be no reason why the latter should not be allowed freedom after dark. Bleaching of the skin is a common result of the disease. The case was a strong one — so strong that I determined to act as if it were actually proved. When on arriving here I noticed that Ralph, who carries out the meals, had gloves which are impregnated with disinfectants, my last doubts were removed. A single word showed you, sir, that your secret was discovered, and if I wrote rather than said it, it was to prove to you that my discretion was to be trusted.”
I was finishing this little analysis of the case when the door was opened and the austere figure of the great dermatologist was ushered in. But for once his sphinx-like features had relaxed and there was a warm humanity in his eyes. He strode up to Colonel Emsworth and shook him by the hand.
“It is often my lot to bring ill-tidings and seldom good,” said he. “This occasion is the more welcome. It is not leprosy.”
“What?”
“A well-marked case of pseudo-leprosy or ichthyosis, a scalelike affection of the skin, unsightly, obstinate, but possibly curable, and certainly noninfective. Yes, Mr. Holmes, the coincidence is a remarkable one. But is it coincidence? Are there not subtle forces at work of which we know little? Are we assured that the apprehension from which this young man has no doubt suffered terribly since his exposure to its contagion may not produce a physical effect which simulates that which it fears? At any rate, I pledge my professional reputation — But the lady has fainted! I think that Mr.