A Medical Doctor’s Sabbatical to Do Science Experiments

A forgotten name in science

Key contributions to scientific knowledge are almost always intertwined with the names of the scientist(s) who made those contributions. A glaring exception exists in the case of one of the most fundamental discoveries of all in the life sciences – photosynthesis.

Jan Ingen-Housz (1730-1799) was a Dutch physician who, at some points in his career served as the family doctor to the royal houses of England and Austria. He was interested in science and kept himself informed of the most recent advances in science, but did not have the time or equipment to do experimental work himself.

Jan Ingen-Housz
(Public Domain)

Through his reading, Ingen-Housz came to know about the work of Joseph Priestley on different kinds of gases (yes, Priestley again!). One experiment of Priestley’s particularly caught his imagination.

Priestley stumbles upon the action of plants on air

It was well known at the time that a candle covered by a glass jar got extinguished in a few seconds. Remember, this was before the modern understanding of oxygen and combustion, so Priestley and his contemporaries thought of it as burning “reducing the quality of air”. They knew that air in which a candle had burned out could not support life either.

This made Priestley wonder why it was that the air in nature did not permanently “go bad”. So many animals and human beings breathed in it and numerous forest fires burned year after year. What was nature’s secret way of purifying the air and making it breathable again?

In August 1771, Priestley carried out several experiments in his attempt to answer this riddle, some of which might seem laughable to us today. In one such experiment, Priestley kept a mint plant in a jar in which a candle had burned out. After 10 days, he took the mint plant out, taking care to ensure that the air in the jar did not mix with the air outside. When he introduced a lighted candle into this jar, it continued to burn just as if the air in the jar had been fresh air from outside.

Priestley’s confusion and Ingen-Housz’s clarity

Priestley should have discovered photosynthesis at this stage, but he didn’t. He did write a report on his experiment, but when other scientists tried to replicate his experiment, they failed to get the same result. They wrote back to him saying they weren’t convinced, and when Priestley tried repeating his own experiment, his own results this time were mixed. His confidence was shaken, though he continued to believe that plants had the power to purify air.

(Any guesses what Priestley was missing?!)

Ingen-Housz had come to know of Priestley’s experiment in 1773, but it was only in 1779 that Ingen-Housz finally managed to take the vacation he had been longing for. For six long years he had turned around in his mind the question of plants’ action on air. And that had prepared him to grab the opportunity to do his own experiments in spectacular fashion.

In the summer of 1779, Ingen-Housz went to stay in the English countryside and in a short three-month period, completed over 500 experiments that would form the body of his book, Experiments Upon Vegetables.

Ingen-Housz made several key discoveries that collectively form the bulk of our modern understanding of photosynthesis. However, two specific insights stand out, since they dispelled the mists of confusion that clouded Priestley’s ambiguous experiments.

Ingen-Housz realised that plants ‘improve the quality of air’ only in the presence of sunlight. In the dark, they reduce the quality of air, just like animals do. Furthermore, he recognised that only the leaves of plants had the ability to improve the air, while other parts like roots, flowers and fruits breathed like animals did.

He also showed that most of the dry weight of the plants came from the components of air that were ‘fixed’ during this process. In other words, plants were mostly “solidified air”!

Fading away into oblivion

It’s interesting to wonder why we don’t remember Jan Ingen-Housz the way we do numerous other scientists who made momentous discoveries. That’s the subject of an entire paper that was presented at a conference of the European Philosophy of Science Association in 2007.

It seems that Ingen-Housz was a humble person, keen to avoid fame and preserve his anonymity. Also, though he formulated most of the concepts of what we understand as photosynthesis today, the term itself was coined much later, in 1893. Probably we don’t remember Ingen-Housz, because what he discovered did not have a name!

  • Leonard K. Nash. Plants and the Atmosphere. Harvard Case Histories in Experimental Science.
  • Geerdt Magiels. Dr. Jan Ingen-Housz, or why we don’t know who discovered photosynthesis. 1st Conference of the European Philosophy of Science Association.
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