ANTON VAN LEEUWENHOEK (1632-1723)

1674 – Netherlands

Portrait of Leeuwenhoek

Leeuwenhoek was probably inspired to take up microscopy after seeing a copy of HOOKE’s Micrographia, though as a draper he was likely to have already been using lenses to examine cloth.
Unlike Hooke, Leeuwenhoek did not use a two lens compound microscope, but a single high quality lens, which could be described simply as a magnifying glass rather than a microscope. Leeuwenhoek is known to have made over 500 of these single–lens microscopes. They are simple devices just a few inches long, with the lens mounted in a tiny hole in a brass plate. The specimen is mounted on a point that sticks up in front of the lens. Two screws move the specimen for focusing. All else that is needed is careful lighting and a very steady, sharp eye.

After an introduction to Henry Oldenburg of the Royal Society in London from Dutch physician and anatomist Regnier de Graaf (discoverer of the egg-making follicles in the human ovary which now bear his name), Leeuwenhoek was encouraged to write to the Society’s journal ‘Philosophical Transactions’.

Leeuwenhoek’s letters were translated into Latin and English from the Dutch and he reported seeing tiny creatures in lake-water.

‘ I found floating therein divers earthly particles, and some green streaks, spirally wound serpentwise, and orderly arranged after the manner of copper or tin worms which distillers use to cool their liquors as they distil over. The whole circumference of each of these streaks was about the thickness of a hair of one’s head ’

Leeuwenhoek’s descriptions of ‘animalcules’ in water from different sources – rainwater, pond water, well water, sea water and so on – were verified by independent witnesses, including the vicar of Delft. Hooke too confirmed his findings with his own observations performed in front of expert witnesses, including Sir Christopher Wren.
Leeuwenhoek came close to understanding that bacteria were germs that cause disease but it took another century before LOUIS PASTEUR made that step.

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ROBERT KOCH (1843-1910)

1876 – Germany

‘Koch’s postulates – four conditions that need to be satisfied to be sure that a particular type of bacteria causes disease’

Koch developed methods of staining bacteria that enabled him not only to see them under a microscope, but also to differentiate between the various strains of microorganisms that he found.

Koch proved that specific organisms cause specific diseases and in addition, that pollution could spread disease.
He developed methods for obtaining pure cultures of bacteria and laid down Koch’s Postulates.

photo portrait of ROBERT KOCH who devised 'KOCH's POSTULATES' ©

ROBERT KOCH

His colleague RICHARD JULIUS PETRI (1852-1921) designed a shallow flat dish that allowed him to grow microorganisms on a solid flat surface, and thus easily separate colonies of bacteria. Until then scientists had grown bacteria in flasks, or injected them into animals.

Koch’s rules for identifying harmful bacteria

  • – the micro-organism must be identified and seen in all animals that suffer the same disease
  • – it must be cultured through several generations
  • – these later generations of bacteria must be capable of causing the disease
  • – the same agent must be found in a newly infected animal as was found in the original victim

Using this set of criteria he identified the organisms responsible for more than twenty diseases, including tuberculosis, salmonella, cholera, pneumonia and meningitis.

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