Ferdinand Julius Cohn

1828-1898

German Botanist and Bacteriologist

Ferdinand Julius Cohn, a German botanist, is recognized today as a founder of bacteriology. He was adept at observing and describing the life cycles of microorganisms. This talent led him, in the 1870s, to construct the first classification system for bacteria.

Cohn was the first of four sons born to Isaac and Amalie (Nissen) Cohn in Breslau, Lower Silesia (now Wroclaw, Poland). His parents lived in Breslau's Jewish ghetto with few financial means until they set up a business selling rapeseed oil for lamps.

Cohn was a precocious child who learned to read by the age of two and began to study natural history at the age of four. He studied at the School of Master Weber from the age of four until six, then entered the Gymnasium of St. Maria Magdelena in 1835. He advanced steadily until the age of 10, when a hearing deficiency arose. Due to this ailment, he suffered from emotional retardation that he did not begin to overcome until 1840. His partial deafness accompanied him throughout his life in spite of the advice and "miraculous remedies" of many doctors. A six-month trip to Berlin with a friend bolstered his ego and upon graduation in 1844, he felt prepared for the freer and more scientific life of the university.

Cohn first attended the University of Breslau as a student in the philosophical faculty, where he studied a wide variety of subjects including astronomy, philosophy, and chemistry. Influenced in part by his professors Heinrich Göppert and Christian Nees von Esenbeck, Cohn chose botany to be his main course of study.

Although Cohn grew up in a period of partial liberation of earlier restrictions on Jews, he was nevertheless barred from the degree examination at Breslau. After several of Cohn's teachers, and his family's friends, failed to obtain a governmental waiver, he transferred to the University of Berlin in October 1846. He eventually regarded this as a fortunate turn of events, for it was in Berlin that he was first introduced, by Johannes Müller (1801-1858), to a new style of natural sciences. During this period, Cohn found a patron in Eilhard Mitscherlich (1794-1863), a chemist who also investigated botanical questions, and met Christian Ehrenberg (1795-1876), who introduced him to the study of microbes. On November 13, 1847, at age 19, Cohn graduated from the University of Berlin with a doctorate in botany.

Cohn remained in Berlin during the turmoil of the 1848 revolution, after which he made his permanent home in Breslau. There he joined the Silesian Society for the Natural Sciences and later directed its botanical section. After 1850, Cohn researched a wide variety of topics including the sexuality of algae and fungi, plant tissues and organs, and the effect of light on microscopic plants. His most lasting influence, however, was his research on bacteria.

In 1850 he was promoted to Privatdocent at the University of Berlin and gained recognition for his work on the microorganism Protococcus pluvialis. This work represents a shift away from the cell theory of Matthais Schleiden (1804-1881) and its focus on organelles located in the protoplasm. In 1854 Cohn published "On the Development of Microscopic Algae and Fungi," in which he reorganized the classification systems of Otto Friedrich Müller (1730-1784), Ehrenberg, and Felix Dujardin (1801-1860). In 1859 Cohn was promoted to extraordinary professor of botany. He married Pauline Reichenbach in 1867.

In 1866 Cohn convinced his university to organize an institute of plant physiology, which he directed. He edited the institute's journal Studies on the Biology of Plants, in which he published his "Investigations on Bacteria." Cohn's research and publications, particularly his proposal that bacteria can be arranged in genera and species, helped to found the study of bacteriology.

LLOYD ACKERT