Charles Robert Richet, a French physiologist, made several experiments testing the reaction of dogs exposed to poison from the tentacles of sea anemones. Some of the dogs died from allergic shock, but others survived their reactions and made full recoveries.

Weeks later, because the recovered dogs seemed completely normal, Richet wasted no time in reusing them for more experiments. They were given another dose of anemone poison, this time much smaller than before. The first time the dogs' allergic symptoms, including vomiting, shock, loss of consciousness, and in some cases death, had taken several days to fully develop. But this time the dogs suffered such serious symptoms just minutes after Richet administered the poison.

Charles Robert Richet used poison from a sea anemone like this one in his experiments on allergies.Corbis

Though Richet was puzzled by what had happened, he realized he could not disregard the unexpected result of his experiment. Later, he noted that his eventual conclusions about the dogs' affliction were "not at all the result of deep thinking, but of a simple observation, almost accidental; so that I have had no other merit than that of not refusing to see the facts which presented themselves before me, completely evident."

Richet's conclusions from his findings came to form the theoretical basis of the medical study and treatment of allergies. He eventually proved that there was a physiological state called anaphylaxis that was the antithesis of prophylaxis: When an allergic subject is exposed to an allergen a second time, he or she is even more sensitive to its effects than the first time. Instead of building immunity to the substance through exposure (prophylaxis), the allergic subject's immunity becomes greatly reduced.

In 1913 Richet received a Nobel Prize for his discovery and articulation of diseases of allergy.

The discovery that later allowed researchers to find insulin was an accident.

In 1889, two doctors at the University of Strasbourg, Oscar Minkowski and Josef von Mering, were trying to understand how the pancreas affected digestion, so they removed the organ from a healthy dog.

A few days later, they noticed that flies were swarming around the dog's urine - something abnormal, and unexpected.

They tested the urine, and found sugar in it. They realised that by removing the pancreas, they had given the dog diabetes.