In 1869 Paul Langerhans, a medical student in Berlin, was studying the structure of the pancreas under a microscope when he identified some previously un-noticed tissue clumps scattered throughout the bulk of the pancreas. The function of the "little heaps of cells," later known as the Islets of Langerhans, was unknown, but Edouard Laguesse later suggested that they might produce secretions that play a regulatory role in digestion. Paul Langerhans' son, Archibald, also helped to understand this regulatory role. The term Insulin (CAS NO.9004-10-8) origins from Insel, the German word for islet/island.
In 1889, the Polish-German physician Oscar Minkowski in collaboration with Joseph von Mering removed the pancreas from a healthy dog to test its assumed role in digestion. The result was establishing for the first time a relationship between the pancreas and diabetes. In 1901, another major step was taken by Eugene Opie, when he clearly established the link between the Islets of Langerhans and diabetes.
Over the next two decades, several attempts were made to isolate whatever it was the islets produced as a potential treatment.
Nicolae Paulescu, a professor of physiology at the University of Medicine and Pharmacy in Bucharest was the first one to isolate Insulin (CAS NO.9004-10-8), which he called at that time pancrein, and published in 1921 the work that he had carried out in Bucharest.
On January 11, 1922, Leonard Thompson, a 14-year-old diabetic who lay dying at the Toronto General Hospital, was given the first injection of Insulin .
Purified animal-sourced insulin was the only type of insulin available to diabetics until genetic breakthroughs occurred later with medical research. The amino-acid structure of insulin was characterized in the 1950s and the first genetically-engineered, synthetic "human" insulin was produced in a laboratory in 1977 by Genentech using E. coli. Partnering with Genentech, Eli Lilly went on in 1982 to sell the first commercially available biosynthetic human insulin under the brand name Humulin. The vast majority of insulin currently used worldwide is now biosynthetic recombinant "human" insulin or its analogs.