“We find no test laid down,” says the Supreme Court of Indiana, “by which we can determine with mathematical precision just how much experience a witness must have had, how expert, in short, he must be, to render him competent to testify as an expert.” But it is for the Court to decide, within the limits of a fair discretion, whether the experience of the proposed expert has been such as to make his opinions of any value; mere opportunities for special observation will not be deemed sufficient [287]. While the Court, or Judge, determines the competency of the witness to testify as an expert, the weight to be accorded to his testimony is for the jury to decide. The testimony of an expert is to be weighed and tested like any other kind of evidence, and is to receive just such credit as the jury may think it entitled to. It is intended to enlighten their minds, not control their judgment [288]. The jury are not bound by the opinions of medical experts: they may weigh their opinions like any other evidence. They may act against the greater number of opinions and in favour of the fewer; for the opinion of one expert may, on account of his greater knowledge and experience on the subject, or from his giving further details of the case, or more probable reasons for his opinions, be of greater value to the jury than the opposite opinions of several [289]. Ordronaux holds that a physician, although confessedly possessing the ordinary experience of his profession, may _quoad_ some particular problem in medical science not be an expert in the best and most critical sense of the term. _Non omnes omnia possumus._ Once received as an expert, |115| the maxim “_Cuilibet in sua arte perito credendum est_,” must be applied, and he cannot be contradicted by any unskilled person [290]. In 1869, the Chief Justice of the Kentucky Court of Appeal well said, that “the opinions of experts not founded on science, but on a mere theory of morals or ethics, whether given by professional or unprofessional men, are wholly inadmissible as evidence.” Hence the opinion of even physicians that no sane man in a Christian country would commit suicide, not being founded on the science or phenomena of the mind, but rather a theory of morals, religion and future responsibility, is not evidence [291]. In the matter of expert testimony, as in other matters, the law does not recognize any particular school of medicine to the exclusion of others. The popular axiom that doctors differ is as true now as ever it was, and so long as it continues to be so, it is impossible for the law to recognize any class of practitioners, or the followers of any particular system, or method of treatment, as exclusively entitled to be regarded as “doctors” [292].