[Van Leeuwenhoek's discovery of bacteria: a look too far ahead]

During the 17th century microscopy was practised at the Royal Society in London by the curator Robert Hooke (1635-1703). He made use of the compound microscope (with uncorrected lenses) and published a book describing the most varied observations of botanical and animal specimens, among which he introduced the concept of 'cellula', observed in botanical material. The useful magnification was limited to 30-40 times. During the same period, the passionate amateur Anthonie van Leeuwenhoek in Delft (1632-1723) was engaged in microscopy, using a so-called simple microscope which was difficult to use but could be applied--albeit with a greater effort--at a much larger aperture so that magnifications in the range of 75-150 times were feasible. Using these self-made instruments, Van Leeuwenhoek was able to observe and describe bacteria, but this could not be confirmed at the Royal Society. It took 150 years before the compound microscope reached this level and bacteria were recognized as pathogenic organisms.