In 1889, a physician noticed a sweet urine clue and helped point medicine toward insulin

Many of the scientific discoveries that revolutionize the field of medicine are made by exploring other issues and questions rather than those they will ultimately be related to. For instance, in 1889, the German physician and pharmacologist Joseph von Mering, together with his colleague Oskar Minkowski, who shared an interest in studying the role of the pancreas in digestion and fat breakdown, conducted some experiments. In order to prove their hypothesis, they performed a surgical intervention on a dog and cut off its pancreas. Although the procedure went successfully, it yielded unexpected results: after some time, the dog began producing larger volumes of urine containing sugar. Although the discovery is rather trivial in modern medicine, it became one of the key elements of diabetes research.

Today’s medical historians recognize the experiment as a watershed in research for what it accomplished by directing scientists’ focus from diabetes as a mere ailment with symptoms to its importance as an ailment centered on an organ: the pancreas. While the researchers in question neither found nor developed insulin, what they did achieve is no less significant – they provided a biological roadmap for further exploration.

A pancreas experiment produced an unexpected result

The famous discovery followed from a practical problem arising in the laboratory rather than from theoretical assumptions about diabetes. As reported in reviews in the Avicenna Journal of Medicine, the debate over the function of the pancreas prompted von Mering and Minkowski to conduct an experiment involving pancreatectomy in dogs. While the scientists aimed to learn more about the process of digestion, the results of their experiment revealed much more than just an aspect of the pancreas's digestive function. Specifically, after removal of the organ, the dog began displaying symptoms of what appeared to be diabetes. The presence of excessive urination and glycosuria (the presence of glucose in the urine), which are typical of diabetes mellitus, is confirmed by Diabetology & Metabolic Syndrome and numerous other reviews on the history of insulin discovery.


Thus, the significance of this finding lay in its association of a particular disease with a specific process occurring within one of our organs. Previously, doctors were able to diagnose diabetes based on the symptoms but had no idea of its biological cause.

The sweet urine clue changed how doctors understood diabetes

It is obvious that today no one questions the pancreas' role in regulating blood sugar levels; nevertheless, insulin was discovered much later, and when Minkowski and von Mering performed their experiments, no one knew anything about it. According to a review article published in the Journal of Clinical Medicine, Minkowski and von Mering's experiments helped develop the concept of a connection between the pancreas and diabetes, which holds that the disease is based not on external factors but on a lack of some function of this organ. It was possible to move from symptoms to the study of the physiological processes underlying them.

This evidence is especially valuable due to its visibility and measurability, as one does not need sophisticated equipment to observe that something occurs after the organ is removed. Moreover, the researchers found clear evidence of the connection between it and carbohydrate regulation; this approach is extremely important for further development. In general, solving medical problems requires understanding the origins of a disease, and Minkowski and von Mering managed to find the place they were looking for.

The discovery helped prepare the path to insulin

Although the relationship between von Mering's work and the discovery of insulin is somewhat indirect, it is quite significant. All historical accounts of diabetes research place von Mering's experiment at the start of a sequence of discoveries that ultimately enabled scientists to isolate insulin in the first decades of the twentieth century. Specifically, as stated in the review in Frontiers in Endocrinology, even though it was Frederick Banting and Charles Best who discovered insulin in 1921, their success relied heavily on prior knowledge of the pancreas's role in diabetes. Without von Mering's and Minkowski's experiments, scientists simply wouldn't have had any idea of where to look for the answers to their questions. Other reviews in Diabetes Therapy and the Journal of Diabetes Research highlight that von Mering's experiment was instrumental in setting the direction of scientific investigation by proving that the pancreas needed to be examined in search of the substance controlling blood sugar.

In hindsight, the surprising thing about the whole story is the humble nature of the observation itself. Surgery was conducted on a dog, and sweet urine was found. Two scientists realized something from this observation. But this tiny bit of knowledge proved sufficient to completely revolutionize an entire field of medicine. By demonstrating the link between diabetes and the pancreas, von Mering and Minkowski gave a little-understood problem biological roots, turning diabetes from a medical mystery into a disease worth investigating by scientists. More than 100 years after its discovery, insulin remains among the most important medicines. Many scientists have made many discoveries since then, but the critical early discovery was made in a laboratory experiment, where the clue to solving the puzzle was found in a dog's urine.