On being called, the medical witness enters the witness-box and takes the oath. This is very generally done by uplifting the right hand and repeating the oath (Scottish form), or by kissing the Bible, or by making a solemn affirmation. 1. He may be called to give _ordinary evidence_ as a _common witness_. Thus he may be asked to detail the facts of an accident which he has observed, and of the inferences he has deduced. This evidence is what any lay observer might be asked. 2. _Expert Witness._--On the other hand, he may be examined on matters of a technical or professional character. The medical man then gives evidence of a skilled or expert nature. He may be asked his opinion on certain facts narrated--_e.g._, if a certain wound would be immediately fatal. Again, he may be asked whether he concurs with opinions held by other medical authorities. In important cases specialists are often called to give evidence of a skilled nature. Thus the hospital surgeon, the nerve specialist, or the mental consultant may be served with a subpoena to appear at court on a certain date to give evidence. The evidence of such skilled observers will, it is supposed, carry greater weight with the jury than would the evidence of an ordinary practitioner. Skilled witnesses may hear the evidence of ordinary witnesses in regard to the case in which they are to give evidence, and it is, indeed, better that they should understand the case thoroughly, but they are not usually allowed to hear the evidence of other expert witnesses. In civil cases the medical witness should, previous to the trial, make an agreement with the solicitor who has called him with reference to the fee he is to receive. Before consenting to appear as a witness the practitioner should insist on having all the facts of the case put before him in writing. In this way only can he decide as to whether in his opinion the plaintiff or defendant is right as regards the medical evidence. If summoned by the side on which he thinks the medical testimony is correct, then it is his duty to consent to appear. If, however, he is of opinion that the medical evidence is clearly and correctly on the opposite side, then he ought to refuse to appear and give evidence; and, indeed, the lawyer would not desire his presence in the witness-box unless he could uphold the case. Whether an expert witness who has no personal knowledge of the facts is bound to attend on a subpoena is a moot point. It would be safer for him to do so, and to explain to the judge before taking the oath that his memory has not been sufficiently 'refreshed.' The solicitor, if he desires his evidence, will probably see that the fee is forthcoming.