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.
Josephine Ball
Ball’s research on the role of hormones and behavior was some of the earliest in the field, contemporaneous with work of Willam Caldwell (W.C) Young and preceding the work of Frank A. Beach, both of whom were considered founders of the field of behavioral neuroendocrinology. Ball's first paper in 1926 represented the earliest work on the role of steroid hormones on non-sexual behaviors, in this case learning and memory in rats. Her work on the role of hormones and reproductive behavior in both rats and macaques throughout the 1930's and early 1940's constituted fundamental contributions to the field. Beach once commented at a meeting that if a conference on reproductive behavior had been held in the 1930’s, it would have three participants: W.C. Young, Josephine Ball, and himself. Beach also considered Ball a friend.