It has been said with reference to the New York law that it is absolutely necessary that the witness should be a _duly qualified_ physician;[271] and it has been held that the words “duly authorized” mean those persons who are not prohibited by the penal code from practising, so that an unlicensed physician may be compelled to disclose confidential communications.[272] Whether the same rule would be applied with reference to information obtained in another State by a physician duly authorized to practise there although prohibited from practising in New York, is a question that is suggested as a case within the reason of the law but outside of its letter, and one which does not seem to have been answered. In New York, in an action by a physician for compensation for his services, it was held that a person who merely answered for a physician at his office in his absence, and was not himself a physician, is not a witness whose testimony is privileged.[273] In Missouri it has been held that a drug and prescription clerk is not a privileged witness.[274] The question arose in the same State, whether a dental surgeon is forbidden to testify under the statute, but its determination was not essential to the judgment and it was left unanswered.[275] To establish the privilege it is necessary that the person who insists upon it to exclude testimony should show by competent evidence that the witness belongs to the class privileged under the law.[276] But where the physician testified that he was a regular practising physician and attended in that capacity, and he was not examined further as to his due authority, it was held that a failure to produce his license could not be urged on appeal as reason for compelling him to testify.[277] The Court said that if the privilege were the physician’s he might, if the objection were taken, be required to prove by the best evidence that he was duly authorized, but as it is the patient’s privilege, in the absence of objection to the sufficiency of the proof, the patient is entitled to the benefit of the presumption that the physician had the license which the law requires to entitle him to practise. WAIVER OF THE PRIVILEGE.