Inverted compound binocular microscope with rack-and-pinion focus that moves the circular stage up and down, triple nosepiece, and chrome rod holding a “Monla” lamp with iris and condenser. The inscription on the tube reads “Leitz / WETZLAR / GERMANY / 545535.” That on the eye tube reads “Leitz / WETZLAR / Germany.” While the form was designed for use in crystallography, this example was used by Leonard Hayflick (b. 1928), an American microbiologist who, with colleagues at the Wistar Institute in Philadelphia, developed the WI-38 cell strain. Hayflick also developed an oral polio vaccine, and he discovered the “Hayflick Limit” in cell senescence—that is, the number of generations an in vitro cell line can divided before dying off.