Microscopes Reveal the Microbial World

 The seventeenth century was a time of growing inquiry and excitement about the "natural magic" of science and patterns of our world, such as the laws of gravitation and motion formulated by Isaac Newton (1642-1727). Robert Boyle (1627-1691) performed the first controlled experiments on the chemical conversion of matter. Physicians attempted new treatments for disease involving the application of "stone and minerals" (that is, the application of chemicals), what today we would call chemotherapy. Minds were open to consider the astounding possibility that our surroundings, indeed our very bodies, were inhabited by tiny living beings.

  Robert Hooke observes the microscopic world.

 The first micros copist to publish a systematic study of the world as seen under a microscope was Robert Hooke (1635-1703). As curator of experiments for the Royal Society of London, Hooke built the first compound microscopea magnifying instrument containing two or more lenses that multiply their magnification in series. With his microscope, Hooke observed biological mate-rials such as nematode "vinegar eels," mites, and mold filaments, illustrations of which he published in Micrographia (1665), the first publication that illustrated objects observed under a microscope (Fig. 1.12). Hooke was the first to observe distinct units of living material, which he called "cells." Hooke first named the units cells because the shape of hollow cell walls in a slice of cork reminded him of the shape of monks' cells in a monastery. But his crude lenses achieved at best 30-fold power (30 x), so he never observed single celled organisms.

Antonie van Leeuwenhoek observes bacteria with a single lens.

Hooke's Micrographia inspired other microscopists, including Antonie van Leeuwenhoek (1632-1723), who became the first individual to observe single-celled microbes (Fig. 1.13A). As a young man, Leeuwenhoek lived in the Dutch city of Delft, where he worked as a cloth draper, a profession that introduced him to magnifying glasses. (The magnifying glasses were used to inspect the quality of the cloth, enabling the worker to count the number of threads.) Later in life, he took up the hobby of grinding ever stronger lenses to see into the world of the unseen. Leeuwenhoek ground lenses stronger than Hooke's, which he used to build single-lens magnifiers, complete with sample holder and focus adjustment (Fig. 1.13B). First he observed insects, including lice and fleas; then the relatively large single cells of protists and algae; then ultimately bacteria. news on Microscopes Reveal the Microbial World One day he applied his microscope to observe matter extracted from between his teeth. He wrote, "To my great surprise [I] perceived that the aforesaid matter contained very many small living Animals, which moved themselves very extravagantly." Over the rest of his life, Leeuwenhoek recorded page after page on the movement of microbes, reporting their size and shape so accurately that in many cases we can determine the species he observed (Fig. 1.13C).
          He performed experiments, comparing, for example, the appearance of "small animals" from his teeth before and after drinking hot coffee. The disappearance of microbes from his teeth after drinking a hot beverage suggested that heat killed microbes a profoundly important principle for the study and control of microbes ever since. Ironically, Leeuwenhoek is believed to have died of a disease contracted from sheep whose bacteria he observed. Historians have often wondered why it took so many centuries for Leeuwenhoek and his successors to determine the link between microbes and dis-ease. Although observers such as Agostino Bassi de Lodi (1773-1856) noted isolated cases of microbes associated with pathology (see Table 1.2), the very ubiquity of microbes most of them actually harmless may have obscured their more deadly roles. In addition, it was hard to distinguish between microbes and the single-celled components of the human body, such as blood cells and sperm. It was not until the nineteenth century that human tissues could be distinguished from microbial cells by the application of differential chemical stains (discussed in Chapter 2).