Sam Cullen Arnett, Jr., South Plains physician, son of Sam Cullen and Alice Ford (Helpman) Arnett, was born at the Arnett ranch headquarters, presently the site of Meadow, Texas, on August 26, 1908. The elder Arnett was a scion of a prominent pioneer ranching family. Young Arnett attended Texas Technological College (now Texas Tech University) the first two years the school was open (1925–27), transferred to the University of Texas for one year (1927–28), then entered Baylor School of Medicine and received his M.D. degree in 1932. After a two-year internship (1932–34) in Kings County Hospital, Brooklyn, New York, he spent six months in the pathology department of the Mayo Clinic. He earned his board certification in internal medicine in 1945.
During his term at Kings County Hospital, Arnett was sent to Boston to study under Dr. E. P. Joslin, one of the leading pioneers in treating diabetes, to learn the clinical use of insulin in the treatment of that disease. After his tenure with Joslin, Arnett returned to Kings County Hospital and set up a diabetes clinic. There he gained expertise in insulin therapy, which he brought to Lubbock. He also introduced the electrocardiograph to Lubbock-the only such instrument within hundreds of miles.
Arnett returned to Lubbock in 1935 and contributed greatly to Lubbock's development as a medical center for the South Plains. In the 1930s Lubbock was not the easiest place to establish a practice. Both hospitals in the city had closed staffs; physicians had either to buy a share of a hospital or to be salaried employees. As part of their refusal to do either, Arnett and doctors Olan Key and Frank B. Malone built their own hospital. The group purchased an acre of land near the Texas Tech campus from W. L. (Bill) Ellwood, of the ranching family for which Arnett's grandfather had worked, and built the most modern hospital in West Texas, using the Ellwoods' old swimming pool as the basement for their twelve-bed facility. The hospital, named Plains Hospital, was opened in 1937. It had modern equipment and was one of the first air-conditioned buildings in Lubbock and reportedly the first completely air-conditioned hospital in Texas. In 1939 the partners sold the hospital to the Sisters of St. Joseph, of Orange, California, who renamed it St. Mary of the Plains Hospital. Arnett continued his active participation in the institution. St. Mary's continued to grow and was moved to its present site bordering Maxey Park in 1970.
Arnett donated twenty acres of land for the campus of Lubbock Christian College and gave the college the "old Arnett home," which was used at varying times for classrooms, as a dormitory, and as the college's administration building. He was also a leader in the move to found a medical school in Lubbock. After Texas Tech University School of Medicine was established, St. Mary's was the major teaching facility in Lubbock for several years. Arnett endowed a chair in the Department of Medicine at Texas Tech University Health Science Center.
He married Olga Wirchniansky in New York on October 31, 1934. They had two children. Arnett died on February 13, 1985, in the hospital he had started in 1935.