O’Brien (plaintiff) was an emigrant passenger on a steamship on her way to Boston. Once in Boston, only individuals with a certificate of vaccination were allowed to go ashore without being detained in quarantine. Cunard Steamship Company (Cunard) (defendant) customarily vaccinated all emigrants who wished to be vaccinated and provided them with a certificate of vaccination. Notices in this regard were posted on the ship in various languages. Approximately two hundred female passengers, including O’Brien, assembled to be vaccinated. The women formed a line to wait for the surgeon to examine each of their arms to determine if they had been previously vaccinated. O’Brien’s turn came and she showed the surgeon her arm. The surgeon informed her that she needed to be vaccinated. In response, O'Brien informed the surgeon that she had been vaccinated previously but it did not leave a mark on her arm. The surgeon then told O’Brien that he should vaccinate her again. O’Brien never told the surgeon that she did not want to be vaccinated. Subsequently, O’Brien held her arm up and was vaccinated by the surgeon, and the surgeon gave O’Brien a certificate of vaccination. After the vaccination, O’Brien experienced complications at the site of the vaccination and blistering all over her body. O’Brien sued Cunard for assault and the trial court directed a verdict for Cunard. O’Brien appealed to the trial court’s ruling to the Supreme Court of Massachusetts.