=II. Expert witnesses concerning their Opinions.= They state the major premiss of the syllogism, whose conclusion is found in the verdict of the jury. All expert witnesses should be skilled witnesses. Experts sometimes become common witnesses when examined as to exhibits produced in court. The weakness of expert testimony is, in practice, its _ex parte_ nature. Medical men called to give evidence as to fact, must beware of being unconsciously drawn into offering expert testimony. I. PREPARING AND GIVING EVIDENCE. =A. BEFORE ENTERING COURT.= Notify directly to the Coroner all deaths, the certificate of the cause of which you are unable to sign (persons found dead—whose death was caused or hastened by accident or injury—who have died without recent medical attendance—who, although attended by a registered medical practitioner during the last illness, have died in such a manner or at such a time, that the medical man is unable to assign a cause of natural death, or for some good reason declines to certify the cause). Most of the cases in which you give medical evidence are those in which you have declined to sign a certificate of the cause of death. There are also those cases in which the relatives object to your treatment, and those in which the registrar refers your certificate to the Coroner. The fact that the account for professional services rendered is likely to be unpaid is =not= a good reason for refusing to sign a death certificate. =Decline to give medical certificates= to police-constables or to solicitors’ clerks gratuitously, and without authority being shown. Demand a formal interview by appointment during professional hours with a responsible superior; otherwise you may receive no fees. Volunteer no private information, and express no opinion in public, concerning medico-legal causes with which you are not personally concerned; otherwise you may be _sub-pœna’d_ to support your views. If you know facts which will aid the execution of justice, give a =hint to the police= either yourself or by a medical friend. Give information _viva voce_ or in letters marked “private.” Never write an unofficial opinion. “Do right, and don’t write—then fear nothing.” Should you receive threatening letters, demanding blackmail, or otherwise without reasonable cause, at once put them into a good solicitor’s hands. “Let this action be a lesson for all men to stand boldly forward—to stand on their character—and not, by compromising a present difficulty, to accumulate imputations on their honour.” Associate yourself permanently with a Medical Defence Society. Unless in self-protection, or at the request of patients, do not appear in court without having been properly served with a formal _sub-pœna_.