_Persons Not Duly Licensed Sometimes Held Not Competent._—It has also been a mooted question in those States where it is necessary, in order to enable a person to practise physic or surgery, that he should be licensed, whether a person practising without a license, however extensive his reading and practice, would be considered qualified as an expert witness in a court of justice. This point, so far as diligent examination discloses, has not been determined in any reported case, although it has been suggested at _nisi prius_ and has been, in one instance within the knowledge of the writer, decided that he is not to be considered an expert in matters involving medical knowledge and skill. The reasoning of the court was that the policy of the State is to prohibit persons not possessing the qualifications required to obtain a license, from acting in any capacity as professors and practitioners of medicine or surgery. If the witness is a member of the profession, legally qualified as such, it has been held that he is sufficiently qualified as an expert if he shows that he possesses the average ability of members of his profession. Hall _v._ Costello, 48 N. H., 176; Tellis _v._ Kidd, 12 Ala., 648; Wharton on Evidence, Sec. 446; Rogers on Expert Testimony, Secs. 17 and 18; Slocovich _v._ Orient Mutual Ins. Co., 108 N. Y., 56. As to the question whether it is necessary that the witness should actually have practised his profession, see the last-cited text-writer, Secs. 43 and 44, who seems to have entertained views opposite to those stated by Professor Greenleaf. Wharton on Evidence, Sec. 439, states the rule as follows: “He must have special, practical acquaintance with the immediate line of inquiry more than a mere vague, superficial knowledge. But he need not be acquainted with the _differentia_ of the specific specialty under consideration.... A general knowledge of the department to which the specialty belongs would seem to be sufficient.” _Interested Persons may still Testify as Experts._—Since the law forbidding interested persons from being witnesses has been changed, it has been suggested that an interested person although otherwise qualified might not be a competent witness to give an opinion as an expert. But the established doctrine is that he may give such an opinion; the weight of it, however, would be for the jury to determine. Greenleaf on Evidence, Redfield’s edition, Sec. 440, citing Lockwood _v._ Lockwood, 2 Curtis, 309; Dillon _v._ Dillon, 3 Curtis, 96, 102. See also Dickinson _v._ Fitchburg, 13 Gray, 546.