The first person to observe living cells was a Dutch trader named
Anton van Leeuwenhoek. Leeuwenhoek made microscopes that
were simple and tiny, but he ground lenses so precisely that the
magnification was 10 times that of Hooke's instruments. In 1673,
Leeuwenhoek, shown in Figure 4-2a, was able to observe a previously
unseen world of microorganisms. He observed cells with
green stripes from an alga of the genus Spirogyra, as shown in
Figure 4-2b, and bell-shaped cells on stalks of a protist of the genus
Vorticella, as shown in Figure 4-2c. Leeuwenhoek called these
organisms animalcules. We now call them protists.