Ferdinand Julius Cohn

German botanist and bacteriologist

• Born: January 24, 1828
• Birthplace: Breslau, Lower Silesia, Prussia (now Wrocław, Poland)
• Died: June 25, 1898
• Place of death: Breslau, Lower Silesia, Prussia (now Wrocław, Poland)

Cohn is considered one of the founders of modern bacteriology. As a botanist, he contributed to understanding the evolutionary position of many microscopic plantlike organisms by elucidating their life histories.

Early Life

The eldest of three sons of a poor Jewish merchant, Issak Cohn, Ferdinand Julius Cohn was born in Breslau’s Jewish ghetto. He was a precocious child who, it is said, was able to read at the age of two and enter school at the age of four. At the age of seven he began higher school at the gymnasium of St. Maria Magdelina, and he began attending the University of Breslau at the age of fourteen. Influenced at the university by professors Heinrich Goeppert and Christian Nees von Esenbeck, he became interested in botany. Because of the rules against Jews receiving advanced degrees at Breslau, he could not be granted one there.

In 1846, Cohn moved to the more liberal University of Berlin, from which, a year later, he obtained a doctorate in botany. At Berlin, he was influenced by several professors, especially Christian Ehrenberg in microscopy and Johannes Müller in physiology. He was in Berlin during the uprisings of 1848, with which he sympathized but in which he did not actively participate. Returning the next year to Breslau at the age of twenty-one, he became a privatdocent at the university, working under Professor Jan Evangelista Purkinje in his Institute of Physiology.

At Breslau, Cohn began his work on the microscopic aspects of living organisms, at that time a new area of biological investigation, particularly because of the newly proposed cell theory of Theodor Schwann and Matthias Schleiden. In 1859, he became an extraordinary professor at the university, and in 1867, he married Pauline Reichenbach. The remainder of his professional career was spent at the University of Breslau, where he became an ordinary professor in 1872.

Life’s Work

Cohn’s primary research interests were in microscopic organisms, both plant and animal, which he used to try to understand their relationships with higher groups of organisms and to understand their development and physiology. At first, he studied various microscopic algae, and, especially using the unicellular Protococcus pluvialis, he concluded that these organisms had a regular life cycle and various developmental phases including sexuality, and that the cellular substance was similar in all cells, both plant and animal. The latter conclusion led him to call the cell substance protoplasm, the name Hugo von Mohl had used for that in plant cells, rather than the term sarcode, which had been used by Felix Dujardin for animal cell substance.

Cohn is best known for his studies of bacteria. He believed that these organisms were more plantlike than animal-like. He showed that they had stable characteristics of form that varied within certain limits, allowing them to be given firm generic names and, at least, provisional specific names. His hesitation about specific names was based on his knowledge that sometimes those of the same form had different fermentative properties. He recognized six genera of bacteria based on their shapes: micrococcus (ball-shaped); bacterium (short rods); bacillus (straight threadlike); vibrio (wavy-shaped); and spirochete (long, flexible spirals). The genera were placed into four larger groups: spaerobacteria for the round ones, microbacteria for the rod-shaped ones, desmobacteria for the longer rod- and thread-shaped ones, and spirobacteria for the wavy or spiral-shaped ones. Because of his clear presentation of the information about the characteristics of bacteria, their cultivation, and their physiology, Cohn helped found the modern science of bacteriology.

Cohn was involved in some of the most important aspects of the developing field of microbiology. He undertook to understand why some bacteria in hay infusions were able to withstand high temperatures. He was able to show that certain bacilli were able to form heat-resistant endospores. This discovery came at a time to help Louis Pasteur, and later John Tyndall, substantiate the attack on the idea of spontaneous generation of microorganisms.

Because he was the major Germanic worker with bacteria, and because he had been trying to prove the importance of bacteria in causing diseases, the then-young Robert Koch wrote to Cohn asking if he could come and demonstrate his evidence for the bacterial cause of anthrax. Koch visited Breslau for three days and convinced Cohn and others at Breslau that he had definite proof that Bacillus anthracis was the sole cause of the disease. Cohn was very impressed with Koch’s ability, supported his research program, and published his paper on anthrax in 1876, in the journal Beitrage zur Biologie der Pflanzen (contributions to the biology of plants), which Cohn had established in 1872 and used to publish many of his own findings.

Work in botany and the popularization of biology also occupied Cohn’s time. From 1856 to 1886, he served as secretary of the botanical section of the Schlesiche Gesellschaft für Vaterländische Cultur (Silesian society for the culture of the fatherland), in which capacity he organized and edited a multivolume work on the cryptogamic flora of Silesia. Cohn wrote a popular work on bacteria, Über Bacterien: Die kleinsten lebenden Wesen (1872; Bacteria: The Smallest of Living Organisms , 1881), and one on plants, Die Pflanze (1882; the plants). In this way, and by articles and lectures, he helped to interest the general public and students in biological subjects. In 1866, he was able to establish an Institute of Plant Physiology at the University of Breslau, the first of its kind in the world, thus fulfilling a long-held dream. He made studies of tissues in plants that were involved with rapid movements that he believed to be similar to animal muscle tissue.

Significance

Ferdinand Julius Cohn is historically important as a major figure in the foundation of modern microbiology, and as a sponsor of Robert Koch in his important studies of disease-causing bacteria. Cohn placed microscopic organisms, particularly algae, fungi, and bacteria, which he considered to be plants, into a Darwinian evolutionary framework. By elucidating their life cycles, and when possible their sexuality, he furthered biological understanding. He recognized the importance of protoplasm as the universal living substance of cells. An important educator, he popularized botany and bacteriology by his writings and lectures.

Bibliography

Brock, Thomas D., ed. Milestones in Microbiology. Englewood Cliffs, N.J.: Prentice-Hall, 1961. Contains English translations of two of Cohn’s important papers, with some deletions. “Studies on the Biology of the Bacilli” is concerned with the survival of spores of some bacteria after boiling; “Studies on Bacteria” describes some of the problems in classifying bacteria, considering them best related to fungi. Comments accompany the papers indicating their historical importance.

Bulloch, William. The History of Bacteriology. New York: Oxford University Press, 1938. Reprint. Mineola, N.Y.: Dover, 1979. Cohn’s work is considered within the context of the history of bacteriology. His studies on the survival of bacteria after sterilization of their media are considered, as are his ideas about bacterial classification.

Cohn, Ferdinand. Bacteria: The Smallest of Living Organisms. Translated by Charles S. Dolley, with an introduction by Morris C. Leikind. Rochester, N.Y.: F. D. Phinney, 1881. Reprint. Baltimore: Johns Hopkins University Press, 1939. Originally published in German by Cohn in 1872, and in a small English edition by the translator in Rochester, New York, in 1881, this introduction to bacteriology was written for the general reader. It gives a brief history of the knowledge of bacteria and presents a summary of what Cohn and others knew and thought about bacteria. The reprint in the Johns Hopkins University Press book contains a short biography and the original complete bibliography of Cohn’s writings.

Geison, Gerald L. “Ferdinand Julius Cohn.” In Dictionary of Scientific Biography. Vol. 3. Edited by Charles Coulston Gillispie. New York: Charles Scribner’s Sons, 1971. This is the only scholarly, substantial biography of Cohn in English. In addition to providing basic biographical information, it stresses Cohn’s importance in the development of microbiology and botany. Provides a detailed bibliography.

Lechevalier, Hubert A., and Morris Solotorovsky. Three Centuries of Microbiology. New York: McGraw-Hill, 1965. Reprint. Mineola, N.Y.: Dover, 1974. Cohn’s place in the development of bacteriology is considered briefly. The authors stress Cohn’s studies of spontaneous generation of microorganisms in relation to Pasteur’s work and the relationship between his work and Koch’s bacterial studies.

Talbott, John H. A Biographical History of Medicine: Excerpts and Essays on the Men and Their Work. New York: Grune & Stratton, 1970. A brief biographical sketch of Cohn, with a composite drawing, stresses his contributions to botany. It includes a long quotation from the English translation of his book, Bacteria: The Smallest of Living Organisms, which emphasizes the importance of bacteria as disease organisms and as possible extraterrestrial initiators of life on Earth.