Sir William Maddock Bayliss (2 May 1860 – 27 August 1924) was an English physiologist.
He was born in Wolverhampton, Staffordshire and gained a B.Sc from London University. He graduated MA and DSc in physiology from Wadham College, Oxford.
Bayliss and Ernest Henry Starling discovered the peptide hormone secretin and peristalsis of the intestines. The Bayliss Effect is named after him. He was also involved in the Brown Dog affair, successfully suing Stephen Coleridge for libel over accusations he made about Bayliss's vivisection work.
In 1893 Bayliss married Gertrude Ellen Starling, the sister of Ernest Starling.
Bayliss was elected a Fellow of the Royal Society in June 1903. He jointly delivered their Croonian lecture in 1904 and was awarded their Royal Medal in 1911 and their Copley Medal in 1919. He was knighted for his contribution to medicine in 1922.
Bayliss died in London in 1924.
The Bayliss and Starling Society was founded in 1979 as a forum for scientists with research interests in central and autonomic peptide function.
In addition to his original scientific research he also published an influential textbook of physiology, Principles of General Physiology, first published in 1915, continuing through to a 4th edition in 1924.
His son, Dr Leonard Ernest Bayliss FRSE (1901-1964) was also a physiologist. who continued the family tradition of writing physiology textbooks.