The German Genius

fibres…The basic cellular tissue is again clearly analogous to that of plants which, as is well known, is almost entirely composed of granules or cells.” 32 His other contribution was to use the word “protoplasma” to describe the basic “ground substance” of cells.
    In November 1832, Karl Asmund Rudolphi, professor of anatomy and physiology at the University of Berlin, died. The vacant chair was occupied the following year by a man who was to become one of the more famous nineteenth-century biologists, Johannes Müller. 33 In 1835 Müller published a monograph on the comparative anatomy of the myxinidae (hagfish), in which he described the similarity between cells in the notochord (the neural channel in the spine) and plant cells. This was a crucial observation, all the more so as Theodor Schwann became Müller’s assistant. Schwann would capitalize on Müller’s insight but only after his momentous meeting with the botanist Matthias Jakob Schleiden.
    Schleiden’s career had followed a familiar pattern. He first took up legal studies, obtaining a doctorate at the University of Heidelberg in 1827. 34 He didn’t enjoy legal work, however, and changed professions, beginning a degree in natural science at Göttingen in 1833 and subsequently transferring to Berlin. Schleiden was invited to work in Müller’s laboratory and it was there that he met Theodor Schwann.
    Though a late convert to botany, Schleiden was always very keen on the microscope and played an important role in its introduction in biological research. (He is thought to have had a hand in the establishment of the Zeiss optical works in Jena.) 35 In 1838 Schleiden released “Beiträge zur Phytogenesis” in Müller’s Archiv , a journal that the Berlin professor had started and that had become one of the most respected periodicals of the time. This article, immediately translated into English and French, was the first airing of the cell theory, which, according to tradition, was conceived in a conversation between Schleiden and Schwann on the subject of phytogenesis. Schleiden was impressed by Robert Brown’s identification of the cell nucleus (1832) and used that as his starting point. The nucleus was then called the cytoblast, and according to Schleiden, “as soon as the cytoblast reaches its final size, a fine, transparent vesicle forms around it: this is the new cell.” Schleiden described this cell as “the foundation of the vegetable world.” While this paper clearly announced “the advent of plant cytology,” Schleiden did so by asserting that cells are “ crystallised inside an amorphous primary substance,” which was quite wrong (italics added). Nevertheless, his botany textbook, published in 1842, the Grundzüge der wissenschaftlichen Botanik , gave over a large section to plant cytology, and in so doing transformed the teaching of botany, attracting many people to what they felt was a new science. 36 Schleiden himself never fully appreciated the true significance or role of the nucleus, or cytoblast, but his fellow biologists in Müller’s laboratory more than made up for this shortcoming.
    His friend and colleague Theodor Schwann was a biologist for fifty years yet devoted only five of those years (1834–39) to the subject for which he is best known. Schwann’s most famous monograph was published the very same year, 1838, in which Schleiden released his “Beiträge” article. Schwann began by outlining the structure and growth of the cells of the notochord and of cartilage. He did so, Schwann said, because their architecture “most closely resembles” that of plants and because cell formation from the “Cytoblastem” is clearly demonstrated. The second section bore a title that reflected his argument and tone: On cells as the foundation of all tissue in the animal body . Purkyne and others had, of course, described cells in many tissues and had speculated that they might be fundamental entities, but Schwann was the first to categorically assert that cells were basic. 37
    After that, his book surveyed what was by then a lot of histological evidence to support the thesis: he discussed cells attached to each other (the epithelium, nails, feathers, and the crystalline lens); cells where the walls are amalgamated with the intercellular substance (cartilage, bone, and teeth); and cells giving rise to fibers (connective and tendinous tissue). Not everything he had to say was accurate but his main purpose was