Jan Ingenhousz: Scientist Who Discovered Photosynthesis

Jan Ingenhousz
Jan Ingenhousz.

 Hulton Deutsch/Corbis Historical/Getty Images

Jan Ingenhousz (December 8, 1730 - September 7, 1799) was an 18th century Dutch physician, biologist, and chemist who discovered how plants convert light into energy, the process known as photosynthesis. He is also credited with discovering that plants, similar to animals, undergo the cellular respiration process.

Fast Facts: Jan Ingenhousz

  • Born: December 8, 1730, in Breda, Netherlands
  • Died: September 7, 1799, in Wiltshire, England
  • Parents: Arnoldus Ingenhousz and Maria (Beckers) Ingenhousz
  • Spouse: Agatha Maria Jacquin
  • Known For: Discovery of photosynthesis and inoculating Hapsburg family against smallpox
  • Education: MD from the University of Leuven
  • Key Accomplishments: Discovered the photosynthetic process and was a leading proponent of variolation in the mid to late 1700s. Elected to the Royal Society of London as a fellow in 1769.

Early Years and Education

Jan Ingenhousz was born in Breda, Netherlands, to Arnoldus Ingenhousz and Maria (Beckers) Ingenhousz. He had one older brother, Ludovicus Ingenhousz, who became an apothecary.

Little information about Ingenhousz's parents survived, but it is generally believed that they were able to provide their sons with what would have been considered an outstanding early education at that time.

At around the age of 16, Ingenhousz completed the Latin school in his hometown and began studying medicine at the University of Leuven. He received his medical degree in 1753. He also did advanced studies at Leiden University. During his time at Leiden, he interacted with Pieter van Musschenbroek, who invented the first electrical capacitor in 1745/1746. Ingenhousz would develop a lifelong interest in electricity as well.

Career and Research

After his university studies, Ingenhousz began a general medical practice in his hometown of Breda. While the practice was successful, Ingenhousz was curious about a number of scientific subjects and kept up with experiments in the sciences in his off hours. He was greatly interested in physics and chemistry, particularly in the study of electricity. He studied the electricity generated by friction and developed an electrical machine, but continued to practice medicine in Breda until the death of his father.

After his father's death, he was interested in studying inoculation techniques, particularly those concerning smallpox, so he traveled to London and became known as a competent inoculator. Ingenhousz helped to inoculate some 700 villagers in Hertfordshire to stop a smallpox epidemic, and he also helped to inoculate King George III's family.

Around this time, the Austrian Empress Maria Theresa became interested in inoculating her family against smallpox after one of her family members died from the disease. Due to his reputation and prior work in the field, Ingenhousz was selected to perform the inoculations.

The inoculation of the Austrian Royal family was successful and he then became the Empress' court physician. Due to his success in inoculating the royal family, he was greatly revered in Austria. At the request of the Empress Maria Theresa, he then went to Florence, Italy, and inoculated the man who would become Kaiser Leopold II.

Ingenhousz was very successful with his inoculation work and was one of the leading proponents of variolation, which derives its name from the scientific name for smallpox, variola. Variolation was an early method for immunizing against the disease. Over time, vaccination against smallpox became the norm, but at the time, Edward Jenner and others used an animal infection, cowpox, to vaccinate humans to protect them from smallpox. Those who were infected with cowpox were then also immune if they were later exposed to smallpox. Ingenhousz's work helped with the reduction in deaths from smallpox, and his methods served as a transition to the vaccines used today. While variolation used a live virus, typical vaccination methods used today use attenuated (weakened) or inactivated viruses, which makes them much safer.

While he was very successful in this field, the stress was immense and his health began to suffer. He stayed in Florence for some time for health reasons. During this time he visited with Abbe Fontana, a physicist. This visit helped to peak his interest in the mechanisms of gas exchange in plants.

In 1775, Ingenhousz married Agatha Maria Jacquin in Vienna.

Photosynthesis Discovery

In the late 1770s, Ingenhousz moved to Calne, a small town located in Wiltshire, in the southwestern portion of England, where he turned his attention to plant research. His colleague Joseph Priestley had discovered oxygen there a few years prior and Ingenhousz conducted his research at the same place.

During his experiments, he put various plants underwater in transparent containers so that he could observe what was happening. He noticed that when the plants were in the light, bubbles appeared under the leaves of the plants. When the same plants were placed in the darkness, he noticed that the bubbles stopped forming after some time. He also noted that it was the leaves as well as other green portions of the plants that were producing the bubbles.

He then collected the bubbles of gas produced by the plants and conducted a number of tests to attempt to determine its identity. After a great many tests, he found that a smoldering candle would reignite from the gas. Thus, Ingenhousz deduced that the gas was oxygen. During his experiments he also deduced that these same plants released carbon dioxide when they were in the dark. Lastly, he noted that the overall amount of oxygen that the plants give off in the light was more than the carbon dioxide released in the dark.

Ingenhousz published "Experiments upon Vegetables, Discovering Their Great Power of Purifying the Common Air in the Sunshine, and of Injuring it in the Shade and at Night" in 1799 before his death. His work was translated into several languages and led to the foundation of our modern understanding of photosynthesis.

Death and Legacy

Ingenhousz's work on the photosynthetic process allowed others to detail the intricacies of the process by building on his work.

While Ingenhousz is most known for his work with photosynthesis, the diversity of his work allowed him to make valuable contributions in a number of scientific areas. He is credited with discovering that plants, like animals, undergo cellular respiration. In addition, Ingenhousz studied electricity, chemistry, and heat conduction.

Ingenhousz also noted the movement of coal dust in alcohol. This movement would come to be known as Brownian motion, for the scientist who is generally credited with the discovery, Robert Brown. While Brown is credited, some believe that Ingenhousz's discovery predated Robert Brown's by approximately 40 years, thus changing the scientific discovery timeline.

Jan Ingenhousz died on September 7,1799 in Wiltshire, England. He had been in ill health for quite some time prior to his death.


  • “Jan Ingenhousz.” Biography, www.macroevolution.net/jan-ingenhousz.html. 
  • Harvey, R B and H M Harvey. “JAN INGEN-HOUSZ” Plant physiology vol. 5,2 (1930): 282.2-287, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC440219/
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Bailey, Regina. "Jan Ingenhousz: Scientist Who Discovered Photosynthesis." ThoughtCo, Aug. 28, 2020, thoughtco.com/jan-ingenhousz-4571034. Bailey, Regina. (2020, August 28). Jan Ingenhousz: Scientist Who Discovered Photosynthesis. Retrieved from https://www.thoughtco.com/jan-ingenhousz-4571034 Bailey, Regina. "Jan Ingenhousz: Scientist Who Discovered Photosynthesis." ThoughtCo. https://www.thoughtco.com/jan-ingenhousz-4571034 (accessed June 4, 2023).