Do not fail to attend after receiving a formally served _sub-pœna_, on peril of contempt of court and an action for resulting damages on the part of the litigant calling you as a witness. You need not afford a _precis_ of your evidence. “He [or they] must be satisfied with impromptu answers.” When in doubt or difficulty, seek at once the best legal advice possible. TO ESCAPE ATTENDING AS A WITNESS: =In Coroners’ Courts.= Written certificates are usually accepted in Coroners’ Courts from members of hospital staffs and from general practitioners concerning the absence from ill-health of witnesses or jurymen; the nature of the illness need not be specified. In higher Courts personal attendance and evidence upon oath are necessary. =In Civil Courts.= If an appeal to the solicitor fails, you may state that your memory of the events in question is vague, and when prompted you may find that the facts as known to you are quite hostile to his client’s claim. You may decline to offer “=expert opinions=”—a direct interference with the facts and circumstances of the case alone =qualifies= you as a common skilled witness who is bound to give evidence if required so to do. THE PREPARATION OF EVIDENCE. “More mistakes are made, many more, by not looking than by not knowing.” You must be ready to meet an =exhaustive interrogation= in Court: hence it is essential that a careful clinical or _post-mortem_ examination should be made, with the aid of all reasonable modern apparatus, and that what is known professionally concerning the matters in hand should be revised from modern text-books: your knowledge of pathology must be up-to-date. “You must know a thing before you suspect it, and you must suspect a thing before you find it.” =Remember= you are not a partisan: value accuracy of observation and of statement as you do your professional reputation. You must be prepared to =explain facts and conclusions clearly= to a body of laymen. =Beware= of mistaking a previously formed inference for a recollection of actual fact—assumed conclusions sometimes fallaciously suggest the real cause. “The chambermaid, in the background, made out as much of the letter as she could, and invented the rest; believing it all from that time forth as a positive piece of evidence.” _Stat pro ratione voluntas_ is a fallacy to be guarded against. Welcome, and even suggest, =conferences= which will avoid subsequent public differences in medical opinions. Decide what exhibits and sketches you will hand in. Label, initial, and number them. If they are returned to you after the trial, preserve them for possible future use (e.g., pathological specimens). Previous to the trial keep all notes and exhibits =under lock and key=. =Remember= medico-legal evidence is subject to certain =limitations=—your “facts” may be absolute, or probable, or merely possible (see p. 45).