"When you have eliminated the impossible...

...Whatever remains, however improbable must be the truth."

That little paean to Okham's Razor was given to us by Mr. Sherlock Holmes, Consulting Detective - whose creator, Sir Arthur Conan Doyle was born 150 years ago today - May 22.

The very first Sherlock Holmes novel "A Study In Scarlet" opens with the introduction in a chemistry lab of Dr. John Watson to Holmes.

"You have been in Afghanistan, I perceive," Holmes immediately concludes.

Of course the Afghanistan to which Holmes refers is the 1878 campaign of the British Empire to secure its colonies in South Asia - notably India. Watson had served briefly as a medical doctor and was discharged after taking a bullet to the shoulder.

But exactly how Holmes deduces Watson's history as he shakes his hand for the first time is the very first mystery.

It's a mystery that we've had 122 years to puzzle out.

At the same time, in the opening pages of "A Study In Scarlet," we meet Holmes having just perfected a chemical test that detects the presence of blood.

Forensic science actually does have a test like that - You can see it used all the time on CSI. It's a presumptive test for blood called the Kastle-Meyer test. It can determine that a substance is either 1. Not blood or 2. Probably blood.

Of interest, the Kastle-Meyer test works in a manner very nearly described by Holmes in "A Study In Scarlet" published in 1887. According to Wikipedia, Kastle-Meyer was first described in 1903.

This tells us two things: First, by the time Kastle-Meyer came in to general use by police labs, the mystery-reading public had already seen its like in the pages of detective fiction.

Second: Conan Doyle had somehow encountered the idea at least 16 years before. And though he had himself been a medical doctor by training, it seems rather far fetched to suppose that he dreamed up the idea of the test - else we would remember him today for something other than his greatest creation.

More likely, Conan Doyle had encountered the idea for the test during his research for his novel at a time when the test was unproven. Likely he prodded along its acceptance in forensic science labs, though.

Of course, we really don't need a discussion here about the contributions to crime fiction that Conan Doyle made. Deductive reasoning prompts us at a murder scene to ask about motive and opportunity. Inductive reasoning allows us to put assemble the clues and form a hypothesis about whodunit.

And by the way, Sherlock Holmes never speculated that master of crime fiction cliches: "The butler did it...."

Happy Birthday, Arthur Conan Doyle!!