Of all the hormones - sometimes depicted as "chemical messengers" - only a proportion are connected with evident sexual behaviour. The first hormone was discovered by Ernest Starling at University College, London, on 16 January 1902. He was investigating the origin of the pancreatic juices produced in the intestines to aid digestion. He introduced into the mucus membrane of the small intestine a few drops of hydrochloric acid, whereupon pancreatic juice started to come from the intestine. But how was the intestine stimulated to act under the influence of the acid? Without nerves, it was responding as if nerve impulses were being fed to it. Starling decided that there must be some sort of chemical reflex. With this insight he was on the road to establishing the concept of the chemical communicators, or hormones (from the Greek "hormnein", to set in motion spur on).