 Light microscopes faced another limit, that on magnification (a limitation imposed by the wave length of light). For cell researchers to obtain higher-resolution images that could reveal constituents of cells, a microscope relying on different physical principles was required. The most important alternative to the light microscope for studying cells was the (transmission) electron microscope, which employs beams of electrons to create images in a manner comparable to photography: locations on the photographic plate hit by many electrons are black in the negative and white in the positive image. When structures in the cell scatter electrons, the location in the negative remains white and appears dark in the positive image. Although electron microscopes were available in the early 1930s, only in the years just before and during World War II did biologists begin to explore their potential. One difficulty they confronted is that most eukaryotic cells are too thick to be penetrated by the 50kV electron beam available in the first electron microscopes. Microtomes had been developed for cutting slices of cells for light microscopy, but new approaches to microtome design were required to slice cells sufficiently thinly without creating distortions. This problem was not solved until the early 1950s (Porter &amp; Blum 1953). Accordingly, some of the first electron micrograph studies focused on fibrous material such as collagen (Schmitt, Hall, &amp; Jakus 1942) or on bacteria (Stanley &amp; Anderson 1941). Porter, Claude, and Fullam (1945) created the first electron micrograph of a eukaryotic cell by culturing it under conditions where the periphery spread very thinly, allowing electrons to penetrate. They generated an image  (Figure 4)  that showed at the periphery 