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by his mentor, Max Schultze, one of the first ‘cell biologists’). From Schulze, Flemming learned constructive criticism, the cautious evaluation of results and the avoidance of speculation — all of which were characteristic of his later scientific work. Other features of his research included careful observation, frequent controls and a thorough evaluation of all results. Flemmingwas also influenced by Rudolf Virchow, one of his academic teachers, and Max Schultze’s students Wilhelm Kühne and Gustav Schwalbe, who implanted in him the idea of the cell as the fundamental, autonomous unit of life. For short periods Flemming assisted in anatomy and histology in Würzburg and Amsterdam until, in 1870, he was offered the position of Prosektor (leader of dissections and anatomicalpreparations) in Rostock. He also taught histology and comparative anatomy, and his students were enthusiastic about his talent for drawing, which brought cells, organs or organisms to life on the blackboard. Indeed, all of his later publications were illustrated by fine detailed drawings that aided understanding (FIG. 2). At the end of 1870 he presented his Habilitation thesis about connectivesubstances and the vessel wall in molluscs, to become Privatdozent (academic teacher). In February 1872 the head of anatomy at Rostock, Wilhelm Henke, asked Flemming to go with him to the German University of Prague, where Flemming was responsible for all histological lectures, seminars and courses. Here, in the same institute as Johannes Evangelista Purkinje, who was considered the father ofhistology, Flemming began his detailed investigations into cell division. Since the German revolution of 1848, nationalism had been growing all over Europe, and Czech students passionately demanded a Czech University in Prague. So the climate became increasingly hostile until most German professors preferred to return to Germany. Although Flemming was not called to the Chair at Königsberg (EastTIMELINE

Walther Flemming: pioneer of mitosis research
Neidhard Paweletz
The German anatomist Walther Flemming began his pioneering studies of mitosis almost 150 years ago. What were his achievements, and where have his discoveries led?

Browsing through the latest issues of cell and molecular biology journals, it is striking how many cover pages show images of dividing cells. This reflects thefact that research into cell division is at the forefront of the field. But what are the origins of this discipline? It began in the seventeenth century, when Hooke1, van Leeuwenhoek2 and others discovered the cellula as a building block of many organisms. Then, in the first half of the nineteenth century, Schleiden3 and Schwann4 established the ‘cell theory’, according to which all organisms arecomposed of tiny units, the cells. Schleiden and Schwann assumed that cells are formed de novo from an intercellular substance in some kind of crystallization (‘free cell formation’) — an assumption that misled many scientists and inhibited research into cell division for almost three decades. For example, in 1875 Strasburger5 published a comprehensive book Ueber Zellbildung und Zelltheilung(“About cell formation and cell division”) in which he defended free cell formation. However, he had abandoned this idea by the time the third edition of his book was published in 1880. By the 1870s, some scientists (such as Dumortier6, von Mohl7, Remak8 and others) had shown that cells multiply by binary fission. At this time, Strasburger’s colleague (and competitor) Walther Flemming (FIG. 1) wasbeginning detailed studies on dividing cells in different organs and organisms, mainly from the animal kingdom. Flemming’s studies were not hampered by the idea of free cell formation, which he no longer believed in, and they eventually led to a solid foundation for modern cellular and molecular biology.
Flemming’s career

Figure 1 | Portrait of Walther Flemming. A welldocumented appreciation of...
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