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.
Herbert McLean Evans
His medical research at Berkeley addressed problems relating to human nutrition, endocrinology, embryology, and histology. In 1918, his research into the number of human chromosomes led him to believe the number to be 48, when most people assumed the number to be much higher. It was only later discovered that the correct figure was 46. Evans had much greater success however with hormones extracted from the anterior lobe of the pituitary gland. He isolated Human Growth Hormone, which is essential for human growth and development. In 1922 along with Katharine Scott Bishop, during feeding experiments on rats, he co-discovered Vitamin E which is needed for human reproduction. Evans became director of the Institute of Experimental Biology at Berkeley in 1931. With Gladys Anderson Emerson, he reported the isolation of the pure Vitamin E from wheat germ in 1937. He also determined the formula CHO. Evans was also instrumental in developing reproductive systems research with Miriam Elizabeth Simpson and Choh Hao Li, by studying the oestrus cycle of rats. Evans is also credited with developing Evans blue, a method which determines blood volume in humans and animals.