Mo. Rev. Stat. § 292.190

All accidents in manufacturing, mechanical, mercantile or other establishments or places within this state where labor is employed which prevent the injured person or persons from returning to work within four days after the injury, or which result in death, shall be reported by the person in charge of such establishment or place to the director of the inspection section or to one of the assistant or deputy inspectors provided for by law, and also to the city or county physician, when there be such an officer, which notice may be given by mail.