Mo. Rev. Stat. § 537.180: Negligence of fellow servant no defense in action by employee against railroad or mine.

Every railroad corporation owning or operating a railroad in this state and every person, company or corporation operating a mine or mines in this state producing lead, zinc, coal or other valuable minerals shall be liable for all damages sustained by any agent or servant thereof while engaged in the work of operating such railroad or while engaged in operating such mine or mines by reason of the negligence of any other agent or servant thereof; provided, that it may be shown in defense that the person injured was guilty of negligence contributing as a proximate cause to produce the injury.