Jan Ingenhousz, Google Doodle celebrates the 277th anniversary of the birth of Dutch physiologist
Jan Ingenhousz or Ingen-Housz FRS (8 December 1730 – 7 September 1799) was a Dutch physiologist, biologist and chemist. 

He is best known for discovering photosynthesis by showing that light is essential to the process by which green plants absorb carbon dioxide and release oxygen.

He also discovered that plants, like animals, have cellular respiration.

In his lifetime he was best known for successfully inoculating the members of the Habsburg family in Vienna against smallpox in 1768 and subsequently being the private counsellor and personal physician to the Austrian Empress Maria Theresa.

He was born into the patrician Ingen Housz family. From the age of 16, Ingenhousz studied medicine at the University of Leuven, where he obtained his MD in 1753. 

He studied two more years at the University of Leiden, where he attended lectures by, among others, Pieter van Musschenbroek, which led Ingenhousz to have a lifelong interest in electricity. 

In 1755 he returned home to Breda, where he started a general medical practice.

In the 1770s Ingenhousz became interested in gaseous exchanges of plants. He did this after meeting the scientist Joseph Priestley (1733–1804) at his house in Birstall, Yorkshire on 23 May 1771. 

Priestley had found out that plants make and absorb gases. Ingenhousz' travelling party in northern England included Benjamin Franklin. In 1779, Ingenhousz discovered that, in the presence of light, plants give off bubbles from their green parts while, in the shade, the bubbles eventually stop.

He identified the gas as oxygen. He also discovered that, in the dark, plants give off carbon dioxide. He realised as well that the amount of oxygen given off in the light is more than the amount of carbon dioxide given off in the dark. This demonstrated that some of the mass of plants comes from the air, and not only the water and nutrients in the soil.

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