By 1903, the U.S. Public Health and Marine Hospital Service has created the following two major categories of medical conditions: "Class A," which are loathsome or dangerous contagious diseases; and "Class B," which are diseases and conditions that render an immigrant "likely to become a public charge."

A subset of Class A conditions includes mental conditions, like "insanity" and epilepsy. Once immigrants arrive at Ellis Island, they are put in a line and "examined" while walking past doctors, who mark their clothes with chalk identifying diagnoses, such as "S" for "senility," and "X" for "insanity." These diagnoses are prescribed as per the doctors' personal views.