Owing to the fact that they often flatly contradict one another, medical experts do not stand very high in popular repute; nevertheless, it is a positive fact that a single medical expert is worth half Scotland Yard in the detection and prevention of crime. Thousands of rivals in love, disagreeable husbands, dangerous political agitators, harsh masters and mistresses, rich uncles, and people of that sort, would be popped off with a few grains of arsenic, or a drop of prussic acid, only that it is well known the doctor has the eyes of a hawk for poison. And, on the other hand, many and many a family is saved from the suspicion attaching to the sudden death of a member, and even many an innocent man from the scaffold, by the proof of natural death which the doctor supplies. Although great poisoning, shooting, stabbing, and other homicidal trials have a wonderful fascination for all newspaper readers, very few fully appreciate the medical evidence, which is usually the most important link in the chain. The evidence is of three kinds--that of the ordinary medical man, who sees the patient dying, perhaps, and performs the post-mortem; that of the chemist, who, in his quiet laboratory, traces the poison or identifies the blood stain; and that of the expert, who gives his inference from the facts stated by the first two. It is these experts who often differ from one another. In a large number of cases the _post-mortem_ examination is the first step in unravelling a mystery. The man who performs it is not to be envied, for the smallest scratch on his hand may admit a dose of deadly poison. [Illustration: THE OLD STYLE DETECTIVE--EXAMINING SCENE OF MURDER.] Many medical men, indeed, wear rubber gloves, and those less careful generally cover their hands with a layer of sticky ointment. It takes from two to four hours to do the job thoroughly. But it is not all cutting up, as most people think. The first thing done is to notice the position of the body, and whether there are any weapons, bottles, or glasses near. Then it is examined from head to toe for scratches, cuts, bruises, moles, tattoo marks. Everything about the hair, eyes, teeth, nose, ears, and other parts, is written down. The height, the age, the muscular development, are all noted. Of course, this inspection alone often reveals the cause of death. Suppose, however, that no external injury is found and no organ is diseased, the suspicion of poisoning naturally arises. In that case, the doctor looks for certain marks that the commonest poisons make, and then he places the stomach and other parts in glass jars, which are securely covered, sealed, labelled, and handed to the analyst. Poisoning is not much favoured by the Briton as a means of killing either himself or anybody else. He generally does the deed in a more open, if more brutal, way. But it is to be feared that a great many more people get rid of undesirable contemporaries in this manner than is popularly supposed.