Hans Jacob was a physician and brain researcher. In 1934, Hans Jacob became a member of the SA and worked in the Main Office for Public Health in the Reich leadership of the NSDAP. As a result, he lost his research grant from the Rockefeller Foundation. From 1935 to 1937, Jacob worked at various institutions in Saxony and eventually became head of the Laboratory for Brain and Nerve Research at the Friedrichsberg Psychiatric Hospital in Hamburg, which was affiliated with the University Medical Centre Hamburg-Eppendorf in 1941. His predecessor in Friedrichsberg was Hermann Josephy, who, as a Jew, had been banned from practising his profession, sent to Sachsenhausen concentration camp and emigrated to the USA in 1936. After the war, Hans Jacob went to Marburg. He continued to publish the results of his research long after the end of the war and, like his colleague Julius Hallervorden, was awarded the Grand Cross of Merit of the Federal Republic of Germany. In 1957, he returned to Hamburg and took over as head of the neurology department at the General Hospital in Altona, while also continuing to supervise the laboratory in Eppendorf, albeit on an honorary basis for another two years.
