Ingenhousz, Jan

Dutch Physician 1730-1799

Jan Ingenhousz made major contributions to plant physiology as well as human medicine. He was born in the Netherlands, received a medical degree in 1753, and went on to further study in Leiden, Paris, and Edinburgh, finally aiding in the discovery of a new smallpox inoculation procedure. For a time he lived in England, where he befriended Benjamin Franklin and Joseph Priestley. After his success with the smallpox vaccine, however, Empress Maria Theresa of Austria called Ingenhousz to the Austrian court. There he served as personal physician to the empress for twenty years. He returned to in England in 1778.

Ingenhousz had an early interest in gases, which led to his interest in photosynthesis. The results of his work demonstrated both the disappearance of gas and the production of oxygen during photosynthesis. Ingenhousz disproved the belief that carbon comes from the soil by establishing a relationship between photosynthesis and plant respiration, claiming that the carbon used by plants came from the carbon dioxide in the air. In addition, he showed that only green leaves have the ability to purify the air through photosynthesis.

In 1778 Ingenhousz conducted experiments on plant production of oxygen. He showed that the green leaves of plants must be exposed to substantial daylight for oxygen production to occur. From this result, he was able to counter the arguments and statements of his contemporary chemists regarding the source of oxygen. Ingenhousz began applying many of the techniques pioneered by Priestley to the study of plant respiration. Priestley had designed a mechanism for measuring oxygen called a eudiometer. Nitric oxide was injected into a closed vessel in which there was already water. A reaction would then occur between nitric oxide and the oxygen in water, producing nitrous dioxide, which is soluble in water. Therefore, the amount of oxygen in the water could be measured by watching the water in the vessel rise.

Using this technique, Ingenhousz showed that plants need the presence of light in order to purify air. In the presence of light, he concluded that "all plants possess a power of correcting, in a few hours, foul air, unfit for respiration; but only in clear light, or in the sunshine."

After he had made this conclusion (what we now call carbon fixation), Ingenhousz began thinking about ways in which oxygen might help respiratory patients; he built some equipment for this purpose but never got terribly far.

In addition to his work on carbon fixation, Ingenhousz performed substantial particle research using algae specimens . His research on algae led to his preliminary observations of what would later be called Brownian Motion and illustrated that lifeless particles show motion. Notably, Ingenhousz was also the first to use thin glass coverslips for liquid preparations viewed under microscopic lenses.

see also Atmosphere and Plants Photosynthesis, Carbon Fixation and; Photosynthesis, Light Reactions and; Physiologist; Physiology; Physiology, History of.

Hanna Rose Shell

Bibliography

Isley, Duane. "Jan Ingenhousz." In One Hundred and One Botanists. Ames, IA: Iowa State University Press, 1994.

Morton, Alan G. "Jan Ingenhousz." In History of Botanical Science. London: Academic Press, 1981.

Van der Pas, P. W. "J. B. Van Helmont." Dictionary of Scientific Biography 6 (1972): 11-16.

Jan Ingenhousz

1730-1799

Dutch Plant Physiologist and Physician

Jan Ingenhousz is best known for his discovery of photosynthesis, the process by which green plants absorb carbon dioxide in the presence of sunlight and release oxygen. Through an ingenious series of experiments, Ingenhousz proved that plant leaves need sunlight rather than heat in order to produce oxygen. He also discovered that plant leaves reverse this process in the dark and release carbon dioxide. Ingenhousz's remarkable observations on plant physiology and photosynthesis were published as Experiments Upon Vegetables, Discovering Their Great Power of Purifying the Common Air in Sunshine, and of Injuring It in the Shade and at Night (1779).

Ingenhousz was born in the Netherlands in 1730. He studied medicine, chemistry, and physics at the universities of Louvain and Leiden. In 1765 he visited London and established a successful medical practice there. He became well known as an early practitioner of inoculation against smallpox. In 1768 he was called to Vienna to inoculate the family of the Austrian empress Maria Theresa. His services were in great demand and he remained in Vienna as court physician and surgeon until 1779, when he returned to London. He was elected a Fellow of the Royal Society in 1769. Although best known for his experiments on plants, Ingenhousz was interested in many other areas of science. He invented a device that could be used to generate large amounts of static electricity and made the first quantitative measurements of heat conduction in metal rods. Ingenhousz carried out many experiments on electricity, magnetism, and the relationship between plants and animals. He died in Wiltshire, England, while visiting the Marquis of Lansdowne's estate.

The experiments on photosynthesis carried out by Ingenhousz were inspired by the work of Stephen Hales (1677-1761) and Joseph Priestly (1733-1804). Hales, the founder of experimental plant physiology, published his classic treatise Vegetable Staticks in 1727. While conducting quantitative experiments on the movement of water in plants, Hales discovered that some component in the air was essential to plant growth. Hales, however, did not fully understand that ordinary air is made up of a mixture of distinct gases. Having isolated and characterized several gases, including "fixed air" (carbon dioxide), Priestley demonstrated that plants have the ability to restore or "revivify" air that has been "damaged" by animal life or by combustion. Green plants, in other words, produce a substance that supports animal life and combustion. Priestley, however, did not always clarify the importance of sunlight in these experiments. Instead, it was Ingenhousz who proved that green plants must be exposed to light rather than heat in order to restore oxygen to the air. He also demonstrated that only the green parts of a plant are capable of performing photosynthesis. While green leaves exposed to sunlight produce large amounts of oxygen, all parts of a plant produce small amounts of carbon dioxide in the dark; plants, like animals, perform respiration and release carbon dioxide into the air. Ingenhousz thus helped to clarify the fundamental similarities and differences between plant and animal life.

LOIS N. MAGNER

Jan Ingenhousz

The Dutch physician, chemist, and engineer Jan Ingenhousz (1730-1799) is noted for his demonstration of the process of photosynthesis in plants.

Jan Ingenhousz was born on Dec. 8, 1730, in Breda. He studied medicine at the University of Louvain and graduated in 1752. After spending some years in several European capitals in the typical 18th-century tradition, he settled in London in 1779 and worked with the celebrated naturalist John Hunter.

In that year Ingenhousz published his important book, 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 this work he anticipated by 2 years Joseph Priestley's discovery of the principles of what is now called photosynthesis, that is, the process by which plants exude oxygen and absorb carbon dioxide, thus purifying the air for animals and man.

Unlike Priestley and other chemists who were working on the characteristics of oxygen from the point of view of chemical philosophy, Ingenhousz was preoccupied by the problem of the fundamental balance in the animal and vegetable kingdoms, and this led him to investigate the mutual interdependence of plants and animals. He introduced the concept that the leaves of plants are great laboratories for cleansing and purifying the air. He also noted that oxygen is emitted by the underside of the leaves and that this is a daylight process, whereas in darkness even plants emit small quantities of carbon dioxide instead of absorbing it. In his reflections at the end of the book, Ingenhousz said, "If these conjectures were well grounded, it would throw a great deal of new light upon the arrangement of the different parts of the globe and the harmony between all its parts would become more conspicuous."

The book was soon translated into many languages and became the foundation of that kind of research which in modern times led to a more basic understanding of the process of photosynthesis; however, his search for the concept of economy or balance in nature was not well understood by his contemporaries. As to the nature and origin of the oxygen which the plant emits, a controversy developed in the 1780s between Ingenhousz and Priestley. Ingenhousz thought that water which plants absorb changes into vegetation and that part of this water is then released as oxygen.

Ingenhousz built electrical machines and invented the plate electric machine. He also wrote a two-volume treatise dealing with problems in medicine which are relevant to the physicist and the medical man, and in a sense it could be said that his basic interest was in what is now called biophysics. Ingenhousz also opposed the theory of subtle electrical fluids and repeated some of the experiments on plant electricity to disprove the accepted view that positive electricity was good for the growth of plants and that negative electricity retarded it.

All of Ingenhousz's scientific work was motivated by a deeply religious attitude and the belief that balance in nature is the best expression of the harmony created by its Author. Ingenhousz died in Wiltshire, England, on Sept. 7, 1799.

Further Reading

Howard S. Reed, Jan Ingenhousz: Plant Physiologist, with a History of the Discovery of Photosynthesis (1949), contains a study of Ingenhousz as well as the text of his famous book. □

Ingenhousz, Jan

Dutch physician and plant physiologist
1730–1799

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.

see also de Saussure, Nicolas; Photosynthesis; Van Helmont, J. B.

Richard Robinson