What is the principle of "ordinary skill" in medical malpractice?

Counsel for the Plaintiffs point out that Lacourciere J.A. qualified this principle in the Brain v. Mado, supra, where, at p. 89-90, he said: … Failure to exercise the ordinary skill of a doctor (in the appropriate speciality, if he be a specialist) is necessary. (Underlining mine)

The last sentence quoted is consistent with the test applied in Canada in medical malpractice cases where negligence is established by proof that the specialist failed to possess or to exercise the reasonable degree of learning and skill possessed by the average specialist in the field. See Wilson v. Swanson, 1956 CanLII 1 (SCC), [1956] S.C.R. 804, at p. 817. Professional opinions expressed have an important bearing on the latter test but, in my view, it is for the trier of fact to weigh the conflicting testimony and ultimately assess the weight to be given to the evidence.