Mo. Rev. Stat. § 292.330

Every employer engaged in carrying on any process or manufacture referred to in section 292.310 shall, as often as once every calendar month, cause all employees who come into direct contact with the poisonous agencies or injurious processes referred to in section 292.310, to be examined by a competent licensed and reputable physician for the purpose of ascertaining if there exists in any employee any industrial or occupational disease or illness or any disease or illness due or incident to the character of the work in which the employee is engaged.