In St. Louis, Iron Mountain & Southern Railroad Co v. Southern Express Company, the Supreme Court of the United States was asked to decide whether a railroad company was liable for damages caused by a collision between two of its trains. The Southern Express Company had sued the railroad company for damages caused by the collision, which had occurred on the railroad's tracks. The Supreme Court held that the railroad company was liable for the damages caused by the collision. The Court reasoned that the railroad company had a duty to exercise reasonable care in the operation of its trains, and that it had failed to do so in this case. The Court also held that the railroad company was liable for the negligence of its employees, even if the negligence was not intentional. The Court concluded that the railroad company was liable for the damages caused by the collision, and ordered it to pay the Southern Express Company for the damages. This case established the principle that a railroad company is liable for damages caused by its negligence in the operation of its trains.

In St. Louis, Iron Mountain & Southern Railroad Co v. Southern Express Company, the Supreme Court was asked to decide whether a railroad company could be held liable for damages caused by an express company that had been hired to transport goods on its railway line. The majority opinion found in favor of the railroad company and held that it was not responsible for any losses incurred due to the negligence of the express company while transporting goods on its railway line. Justice Field dissented from this decision and argued that under common law principles, a carrier is liable for all damage done by their agents or servants while acting within their scope of employment; thus, he believed that the railroad should have been held accountable for any losses suffered as a result of negligent acts committed by employees of the express company during transit over its tracks. He further noted that if carriers are allowed to escape liability simply because they did not directly employ those who were responsible for causing injury or loss then there would be no incentive whatsoever to ensure proper care when entrusting freight with third parties such as express companies.