In the early 20th century, Dr. Henry Plummer developed Mayo Clinic's multi-specialty group practice model and an integrated medical record system. Plummer's system allowed doctors to better share patient information with one another. Prior to Plummer's system, doctors worked in solo practice and shared patient information when necessary either verbally or by letter. Plummer also helped design and fabricate building systems innovations, such as steam sterilization rooms, metal surgical tools and equipment, pneumatic tube system, and knee operated sinks. In 1905, Mayo Clinic advanced a technique of using frozen tissue during surgery to determine if a patient had cancer while the patient was still in the operating room. Mayo Clinic offered the first graduate medical education program in 1915 and the first nonprofit practice aligned with medical education and research. In the 1920s, Dr. Albert Compton Broders of the Mayo Clinic created the first index to grade tumors. Mayo Clinic opened the first hospital-based blood bank in Rochester in 1935. Early in Mayo Clinic's history, the hospital designed the one-legged mobile instrument stand known as the Mayo stand.