Roosters, bending seedlings and cut nerves revealed the body's chemical messengers
In 1849 Arnold Berthold moved a rooster's testis into its abdomen and watched the bird keep crowing and strutting as normal. Location did not matter, he reasoned, so something chemical must be leaking into the blood. That substance, testosterone, was among the first clues that organs talk to each other through molecules.
Berthold's roosters without testes had shrunken combs, a feeble crow and no interest in hens or fighting. Transplanting a testis from a different bird restored everything, ruling out both position and the individual animal's own tissue. His conclusion anticipated a whole field of physiology decades before anyone had a word for it.
Plants supplied a parallel story. Through the 1870s Charles Darwin and his son Francis studied seedlings turning towards light and found that the tip senses the light while the bending happens further down. They proposed a transmissible substance carrying the signal, an idea other botanists brushed aside. In the 1920s Frits Went in the Netherlands and Nikolai Cholodny in Russia, working separately, showed that an unevenly distributed growth hormone causes the curve, and in 1933 Kogl, Haagen-Smit and Erxleben isolated it and called it auxin.
The first animal hormone actually identified was adrenaline, in adrenal extracts studied by George Oliver and Edward Schafer, who reported in 1894 and 1895. Credit is often wrongly given to secretin, which William Bayliss and Ernest Starling found in 1902 after cutting the nerves to a pancreas and discovering that it still responded to food, prompted by a factor carried in blood from the intestine. In 1905 Starling coined the word hormone, from a Greek verb for arousing or setting in motion.
Hormones are defined by what they do rather than what they are made of, so the category is chemically wild. It spans steroids such as oestrogen, proteins such as insulin, amino acid derivatives such as epinephrine and auxin, and even gases such as ethylene and nitric oxide. Water-soluble ones typically dock at the cell surface, while fat-soluble steroids slip inside to switch genes on. Insects add oddities of their own, including juvenile hormone.
Source: Hormone
