Bayliss, William Maddock (1860-1924) was an English biologist who worked in the fiel the of physiology the branch of biology that studies life functions. In 1902, Bayliss and fellow physiologist Ernest Starling were the first scientists to identify a hormone. They observed a hormone produced by the small intestine and called the hormone secretin, because it stimulated the pancreas to secrete digestive juices. In 1905, Starling coined the word hormone, which comes from a Greek term meaning to set in motion .

After attending a private school in Wolver-hampton, Bayliss served as an apprentice-to a local physician. In 1881, he entered University College, London, where he earned his B.S. degree in zoology and physics in 1882. In 1885, he enrolled at Wadham College in Oxford and three years later, he took a doctor's degree in physiology. He then returned to University College as a teaching and research assistant. In 1903, he became an assistant professor, and in 1912, a professor of general physiology, a position he held until his death.

During World War I (1914-1918), Bayliss contributed to the effort by devising a way to replace lost blood with a saline solution and thus prevented many wounded soldiers from dying of surgical shock. In addition to his scientific research, Bayliss wrote Principles of General Physiology (1915), a groundbreaking book that became a standard authority on the subject. It is now viewed as a historically significant volume in the field of biology.

Bayliss married Gertrude Starling, the sister of Ernest Starling. The couple had one daughter and three sons. Bayliss was an experienced photographer and his pictures often illustrated his books and papers. He was knighted in 1922.