Dutch physician and plant physiologist
Jan Ingenhousz was a pioneer in plant physiology and demonstrated that oxygen is produced during photosynthesis. Born in the Netherlands, Ingenhousz practiced medicine in several European countries and served as a court physician to Empress Maria Theresa of Austria for twenty years. Ingenhousz promoted vaccination against smallpox and helped develop a new vaccination procedure.
Ingenhousz used the gas-measuring techniques of his friend Joseph Priestley to study how plants alter the air. Priestley had shown that animals or burning candles "spoil" air, making it unfit for breathing. He had also reported that plants restore the air, but other experimenters could not replicate his results.
Ingenhousz attacked this problem systematically and meticulously. By placing different plant parts in sealed containers either exposed to or hidden from sunlight, Ingenhousz showed that plants do restore the air by the production of oxygen (a gas that Priestley had recently discovered) and that the green leaves must be exposed to sunlight for this to occur. In this way, Ingenhousz began the scientific understanding of photosynthesis, a process elucidated further by Swiss agriculturist Nicolas de Saussure and others. Ingenhousz contemplated using oxygen to treat patients but did not develop the equipment to do so.