Low-Temperature Light Microscopy

Abstract

Low-temperature light microscopy, or cryomicroscopy as it is sometimes referred to, is a powerful technique for investigating the wide range of phenomena associated with freezing and thawing in hydrated systems. Its singular advantage over all other methods is that it allows dynamic observations and analysis to be made under thermally controlled conditions. The technique provides a readily visible and sometimes dramatic view of phase change processes and their effect on cells and tissues. An impressive literature exists on the subject, some of it dating back to the late 19th century. Most of the earlier studies were of an entirely qualitative nature and centered on observing and recording the processes of freezing and thawing in a range of biological tissues. These were heroic times, because the only way cryomicroscopy could be performed was to ensure that the sample, stage assembly, microscope, and observer were all in a cold environment. Cohn (1871) and Kunisch (1880) went outdoors in winter to study the process of freezing in cells of the alga Nitella. Weigand (1906) did the same thing to study freezing in fruit tree buds. The German botanist Sachs (1892) was a little more cautious and put his microscope on an open window sill at 267 K in order to follow the formation of ice crystal formation in pumpkin tissue.