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 Rh innocent and unconscious friends, and, by an extension of the same method, to baffle the criminal and lay bare the manner of his crime. There is nothing new under the sun: Voltaire taught us the method of Zadig, and every good teacher of medicine or surgery exemplifies every day in his teaching and practice the method and its results. The precise and intelligent recognition and appreciation of minor differences is the real essential factor in all successful medical diagnosis. Carried into ordinary life, granted the presence of an insatiable curiosity and fairly acute senses, you have Sherlock Holmes as he astonishes his somewhat dense friend Watson; carried out in a specialised training, you have Sherlock Holmes the skilled detective.

Dr. Conan Doyle's education as a student of medicine taught him how to observe, and his practice, both as a general practitioner and a specialist, has been a splendid training for a man such as he is, gifted with eyes, memory, and imagination. Eyes and ears which can see and hear, memory to record at once and to recall at pleasure the impressions of the senses, and an imagination capable of weaving a theory or piecing together a broken chain, or unravelling a tangled clue, such are implements of his trade to a successful diagnostician. If in addition the doctor is also a born story-teller, than it is a mere matter of choice whether he writes detective stories or keeps his strength for a great historical romance as is the White Company. Syme, one of the greatest teachers of surgical diagnosis that ever lived, had a favourite illustration which, as a tradition of his school, has made a mark on Dr. Conan Doyle's method, "Try to learn the features of a disease or injury as precisely as you know the features, the gait, the tricks of manner of your most intimate friend." Him, even in a crowd, you can recognize at once; it may be a crowd of men dressed alike, and each having his complement of eyes, nose, hair, and limbs; in every essential they resemble each other, only in trifles do they differ; and yet, by knowing these trifles well you make your diagnosis or recognition with ease. So it is with disease of mind or body or morals. Racial peculiarities, hereditary tricks of manner, accent, occupation or the want of it, education, environment of all kinds, by their little trivial impressions gradually mould or carve the individual, and leave fingermarks or chisel scores which the expert can recognize. The great broad characteristics which at a glance can be recognized as indicative of heart disease or consumption, chronic drunkenness or long-continued loss of blood, are the common property of the veriest tyro in medicine, while to masters of their art there are myriads of signs eloquent and instructive, but which need the educated eye to detect. A fair sized and valuable book has lately been written on the one symptom, the pulse; to any one but a trained physician it seems as much an absurdity as is Sherlock Holmes' immortal treatise on the one hundred and fourteen varieties of tobacco ash: The greatest stride that has been made of late years in preventive and diagnostic