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.
Cyril Norman Hugh Long
In the 1930s and 1940s Long and Abraham White worked together in the Yale Medical Center. As a result of their work in 1937 they isolated bovine prolactin, the first of the protein pituitary hormones to be obtained in pure crystalline form. Later, they isolated different hormones, and later characterized and sequenced many of them, greatly contributing to modern biochemistry. Long mainly worked with the hormones of the pituitary gland and adrenal extracts of the metabolism; his major research goal was to find a cure for diabetes.