Secretin
Secretin was the first hormone to be identified. In 1902, William Bayliss and Ernest Starling were studying how the nervous system controls the process of digestion. It was known that the pancreas secreted digestive juices in response to the passage of food (chyme) through the pyloric sphincter into the duodenum. They discovered (by cutting all the nerves to the pancreas in their experimental animals) that this process was not, in fact, governed by the nervous system. They determined that a substance secreted by the intestinal lining stimulates the pancreas after being transported via the bloodstream. They named this intestinal secretion "secretin". Secretin was the first such "chemical messenger" identified. This type of substance is now called a hormone, a term coined by Bayliss in 1905.
Ray Farquharson
Through his research in endocrinology with colleague Arthur Squires, Farquharson discovered what became known as the "Farquharson Phenomenon": that the introduction of continuous exogenous hormone doses suppresses the natural production of that hormone in the patient and causes temporary atrophy in the producing organ. This phenomenon became one of the basic principles of endocrinology and a key factor in the etiology of hormonal abnormalities. Farquharson also made significant contributions related to anemia and pigment metabolism. He was the first Canadian doctor to publicize Sheehan's syndrome, and the first North American to report on Simmond's disease. As an educator and researcher, he was an early promoter of laboratory testing in the evaluation of illness; he was known for advocating both this and awareness of potential psychological issues in patients.