Fourth: He should be honest with his client before the trial in advising him and giving him opinions, and upon the trial should preserve an absolutely impartial attitude, concealing nothing, perverting nothing, exaggerating nothing.
Fifth: On the preliminary examination as to his qualifications as a witness he should be frank and open in answering questions. He should state fully the extent and the limits of his personal experience and of his reading upon the subject, without shrinking from responsibility, yet without self-glorification.
Sixth: He should be simple, plain, and clear in his statement of scientific facts and principles, avoiding the use of technical language, and trying to put his ideas in such form that they will be grasped and comprehended by men of ordinary education and intelligence.
Seventh: He should avoid stating any conclusions or principles of which he is not certain, but having an assurance that he is right he should be firm and positive. He should admit the limitations of his knowledge and ability. Where a question is asked which he cannot answer, he should not hesitate to say so; but he should refuse to be led outside the subject of inquiry, and should confine his testimony to those scientific questions which are really involved in the case, or in his examination of the case.
Eighth: And finally, he should always bear in mind that at the close of his testimony an opportunity is usually given to him to explain anything which he may be conscious of having said, which requires explanation; and partial statements which need a qualification to make them a truth. This is the physician’s opportunity to set himself right with the court and with the jury. If the course of the examination has been unsatisfactory to him, he can then, by a brief and plain statement of the general points which he has intended to convey by his testimony, sweep away all the confusion and uncertainty arising from the long examination and cross-examination, and can often succeed in producing for the first time the impression which he desires to produce, and can present the scientific aspects of the case briefly and correctly.
Probably no man was ever so gifted as to be able in practice to carry out all of these principles in giving medical testimony. If he could, he would be the ideal expert witness. But the principles are, after all, simple and easily followed in the main. Any physician who knows his subject and who has a clear head and the ordinary faculty of expression, by observing these principles can make himself invaluable as an expert witness. There is no branch of the profession which brings a broader fame, greater influence, or larger emoluments than this. There is no branch, on the other hand, in which men of real ability make more lamentable failures.