The observant physician begins to gather information about a patient from the moment he enters the sick-room or the patient steps into his consulting-room; and the value of the information obtained in the first thirty seconds, before a word has been spoken, is sometimes astonishingly great. While no intelligent man would dream of depending upon this first _coup d'[oe]il_, "stroke of the eye" as the French so graphically call it, for his final diagnosis, or accept its findings until he had submitted them to the most ruthless cross-examination with the stethoscope and in the laboratory, yet it will sometimes give him a clew of almost priceless value. It is positively uncanny to see the swift, intuitive manner in which an old, experienced, and thoughtful physician will grasp the probable nature of a case in one keen look at a patient. Often he can hardly explain to you himself how he does it, what are the data that determine it; yet not infrequently, three times out of five, your most elaborate and painstaking study of the case with all the modern methods will bring you to the same conclusion as that sensed within forty-five seconds by this keen-eyed old sleuth-hound of the fever trails. Time and again, in my interne days, have I gone the rounds of the wards or the out-patient departments with some kindly-faced, keen-eyed old Sherlock Holmes of the profession, and seen him point to a new case across the ward with the question: "When did that pneumonia come in?" or pick out a pain-drawn, ashy mask in the waiting line, with an abrupt, "Bring me that case of cancer of the stomach. He's in pain. I'll take him first." And, in later years, I have had colleagues with whom it was positively painful to walk down a crowded street, from the gruesome habit that they had of picking out, and condemning to lingering deaths, the cases of cancer, of Bright's disease, or of locomotor ataxia, that we happened to meet. Of course, they would be the first to admit that this was only what they would term a "long shot," a guess; but it was a guess based upon significant changes in the patient's countenance or gait, which their trained eye picked out at once, and it was surprising how often this snapshot diagnosis turned out to be correct.