All applicants for examination shall undergo a physical examination, which shall be conducted under the supervision of a doctor of medicine appointed by the board of county commissioners. No person shall be eligible for appointment until said doctor certifies to the commission that the applicant is free from any bodily or mental defects, deformity or disease that might incapacitate him from the discharge of the duties of the position desired in the police force or as fireman or fire inspector.
16 P.S. § 4517