FÉLIX DUJARDIN: BIOGRAPHY, CELL THEORY AND OTHER CONTRIBUTIONS - BIOLOGY - 2025

Félix Dujardin (1801 - 1860) was a French biologist known for his studies on the classification of protozoa and invertebrates. He also served as a professor of geology and mineralogy, later on as a professor of zoology and botany at different French universities.

One of his great merits is having been a self-taught person. However, he rigorously studied specialized texts on topics of interest such as biology or cell theory.

Louis Joubin via Wikimedia Commons

For a long time, Dujardin dedicated himself to the research of microorganisms and was the first to propose the creation of the classification of rhizopods, which later became what is now known as protozoa.

Also, Dujardin denied that microorganisms were complete organisms like more complex animals. Likewise, he took advantage of advances in optics to study the subcellular structure of organisms.

Dujardin's name is also known to be one of the first to have described protoplasm. These investigations did not prosper during the time due to the lack of knowledge in other sciences that were fundamental to extend the concept.

Biography

Early years

Felix Dujardin was born on April 5, 1801 in Tours, France. He was the son of a watchmaker who for a time provided him with apprenticeships in the family business, which gave him manual skills that served him for his future occupation.

His first letters were received at the local school. Dujardin had a penchant for the arts until he was introduced to various texts on nature and anatomy from a family friend. Since then his passion for chemistry began to deepen with home experiments.

He could not enter the École Polytechnique, so he decided to dedicate himself briefly to the study of painting.

Autodidact

Despite having landed a position as a hydraulic engineer, Dujardin still had a penchant for the natural sciences.

After marrying Clémentine Grégoire, he returned to his hometown and began working as a librarian, at the same time as he joined the teaching profession. Mainly, he taught mathematics and literature; thanks to that he left his job as a librarian.

It was then that he was able to continue his scientific studies and even published works about fossils in the area.

After teaching subjects such as geometry and chemistry, he decided to specialize in zoology, since it was difficult to carry out work on subjects as diverse as he had done until then. That is why he chose to move to the French capital.

Dujardin was largely self-taught, dabbling in various subjects by immersing himself in the corresponding textbooks.

Zoology

For several years, Félix Dujardin maintained his work as a writer of scientific articles in various publications. During this period he created a book which he baptized as Promenades d'un naturaliste.

It was in the mid-1830s, while studying microorganisms on the southern coast of France, that he came to the conclusion of the existence of rhizopods.

In 1840 Dujardin received the post of professor of geology and mineralogy at the University of Toulouse, and the following year he was professor of zoology and botany at Rennes.

Death

Felix Dujardin passed away on April 8, 1860 in Rennes, France at the age of 59. His last work was related to echinoderms.

It is believed that thanks to his knowledge in other fields of science, he was able to reach the conclusions he reached during his life and that allowed him to achieve so many advances.

Although his work was not popularly appreciated during his life, it was of great value because it could be fully understood by other scientists.

Applied studies

Rhizopods

He worked much of his career with microscopic animal life. In 1834 he proposed that a new group of single-celled organisms be called rhizopods. The name was later changed to protozoa or protozoa.

Protozoa are unicellular eukaryotes, either free-living or parasites, that feed on organic matter, such as other microorganisms, or organic tissues and waste.

Historically, protozoa were considered "unicellular animals", that was because they regularly showed similar behaviors to these.

Among these behaviors were predation or the ability to move, together with the lack of the cell wall that plants and many algae have.

Although the traditional practice of grouping protozoa with animals is no longer considered valid, the term is still used loosely to identify single-celled organisms that can move independently and feed by heterotrophy.

Dujardin refuted naturalist Christian Gottfried Ehrenberg's theory that microscopic organisms were "whole organisms" similar to more complex animals.

Contributions of optics to Dujardin's work

In the seventeenth and eighteenth centuries, microscope lenses were inaccurate due to the optical characteristics of the materials with which they were made, making it difficult to see carefully detailed structures in semi-transparent objects.

In the 19th century, the optics of microscopes were improved by the invention of the achromatic doublet by Chester Moor Hall, John Dolland, and James Ramsdell. That led to the introduction of achromatic lenses in microscopes during the 1820s and 1830s.

Newly developed lenses were corrected to attenuate spherical and chromatic aberrations. That gave Felix Dujardin the opportunity to detect objects that were about 100 times smaller than those that could be seen with the naked eye.

The new microscopes with achromatic lenses provided the means to explore the structure of living things at the subcellular level, and Felix Dujardin was one of the pioneers in putting these new instruments into practice and scientific use.

Invertebrates

In addition to his studies of microscopic life, Félix Dujardin conducted extensive research on invertebrate groups, including echinoderms, helminths, and cnidarians.

Echinoderms

Echinoderms was the common name given to any member of the phylum echinodermata of marine animals. They are recognizable by their radial symmetry, and include such well-known animals as stars, urchins, and sea cucumbers.

Echinoderms are found in all ocean depths, from the intertidal zone to the abyssal zone. The phylum contains about 7000 living species. Their study demonstrated the range and diversity of Dujardin's interests.

Helminths

Helminths, or parasites, were also the subject of great research by Dujardin, as evidenced by his book published in 1845, Natural history of helminths or intestinal worms.

These organisms are macroparasites, which in adulthood can generally be seen with the naked eye. There are abundant intestinal worms that spread through the soil and that impact the gastrointestinal tract.

Dujardin contributed to the discovery that helminths can survive in their mammalian hosts for long periods of time, as they are capable of generating changes in the immune response through the secretion of immunomodulatory products.

Cnidarians

Continuing with marine animals, Dujardin also worked analyzing cnidarians, a phylum of the metazoan kingdom that contains more than 11,000 species of organisms found exclusively in aquatic environments (freshwater and marine).

Their distinctive feature is cnidocytes, specialized cells that they use primarily to capture prey. Their bodies consist of mesoglea, a non-living gelatinous substance, sandwiched between two layers of epithelium that are mostly one cell thick.

In the foraminifera group, he observed the seemingly shapeless life substance exuding out through openings in the calcareous shell and named it "sarcode," later known as protoplasm.

This work led him to refute, in the mid-1830s, the theory that was again in vogue thanks to Christian Ehrenberg that microscopic organisms have the same organs as higher animals.

Cell theory

In the early 19th century, infusoria comprised a wide range of organisms of size and complexity, ranging from bacteria to small invertebrates to worms and crustaceans.

One of the foundations for the advances of Dujardin's studies was the cell theory, which when developed by Theodor Schwann and Mattias Jakob Schleiden, stated that the basis of organisms was the cell. Which indicated that organisms should be made up of one or more cells.

After this approach, the series of advances with respect to the infusoria quickly precipitated. It was in 1841 that Dujardin independently recognized that many protozoa were single cells with a high level of internal organization comparable to plant cells.

Studies on infusoria in the 21st century were dominated by Dujardin's research, along with a select group of biologists made up of Christian Gottfried Ehrenberg, Samuel Hahnemann, Samuel Friedrich Stein, and William Saville-Kent.

Other contributions to biology

Protoplasm

Felix Dujardin had a fundamental role in the development of the concept of protoplasm. In 1835 he described what he saw under the microscope: a gelatinous substance exuding from the broken end of a protozoan (then called an infusoria).

Dujardin described this "living jelly" as a "gelatinous, pulpy, homogeneous substance, without visible organs, and yet organized." Although he gave it the name "sarcoda", the term protoplasm was widely adopted with the passage of time.

Thirty-three years later, in his famous Sunday lecture in Edinburgh on November 8, 1868 and drawing on Dujardin's studies, Thomas Huxley called protoplasm "the physical basis of life."

The discovery of protoplasm inspired the beginning of studies of colloid chemistry. Unfortunately, the understanding of both protoplasm and colloid was hampered by the lack of extensive knowledge about physics and chemistry related to matter during this period.

According to the association induction hypothesis, protoplasm remains the physical basis of life, as noted by Thomas Huxley following Dujardin in the first place and rightly so. This only differs from current theory in that protoplasm is no longer defined by its appearance.

Vacuoles

Felix Dujardin also contributed to the discovery of vacuoles in protozoa. Although the contractile vacuoles or "stars" of many protozoa were first seen by Lazzaro Spallanzani (1776), he mistook them for respiratory organs.

These stars were named "vacuoles" by Felix Dujardin in 1841, although cell sap without optical structure had been observed by botanists for years.

The term vacuole was used for the first time to refer specifically to plant cells in 1842, by Matthias Jakob Schleiden, when he distinguished it from the rest of the protoplasm.

Corpora pedunculata

In 1850 he was the first to describe the corpora pedunculata, a key arrangement in the nervous system of insects. These pedicle bodies make up a pair of structures in the brain of insects, other arthropods, and some annelids.

In botany and zoology, the standard abbreviation Dujard is applied to the species he described, to mark him as the forerunner in taxonomy and scientific classification in certain plants and animals.

Plays

- Memoire sur les couches du sol en Touraine et descriptions des coquilles de la craie des faluns (1837).

- Natural history of zoophytes. Infusoria, including the physiology and classification of these animals, and how to study them under the microscope (1841).

- New manual for the observer of the microscope (1842).

- Natural history of helminths or intestinal worms (1845).

References

1. En.wikipedia.org. (2019). Felix Dujardin. Available at: en.wikipedia.org.
2. Encyclopedia Britannica. (2019). Félix Dujardin - French biologist. Available at: britannica.com.
3. Leadbeater, B. and Green, J. (2000). Flagellates: Unity, Diversity and Evolution. London: Taylor & Francis.
4. Wayne, R. (2014). Plant Cell Biology: From Astronomy to Zoology. Academic Press.
5. Grove, D. (2013). Tapeworms, lice, and prions. OUP Oxford.
6. Pollack, G., Cameron, I. and Wheatley, D. (2006). Water and the cell. Dordrecht: Springer.
7. Encyclopedia.com. (2019). Felix Dujardin - Encyclopedia.com. Available at: encyclopedia.com.