Freezing by Liquid Carbon Dioxide in Making Slides Permanent

The expansion of liquid CO₂ may be employed in a quick-freeze method for making aqueous slide preparations permanent. An apparatus is described for this purpose which could be duplicated satisfactorily by cutting a 22mm square hole in the top of a standard freezing microtome specimen holder. The edges should be filed smooth to provide a flat surface for the slide to rest on, and clamps added to keep the slide in place while freezing. Once the slide is frozen, the cover slip may be readily removed, leaving practically all of the tissue on the slide. Following simultaneous thawing and dehydration of the slide in 95% alcohol, covering is done with Diaphane or Euparal and a clean, dry cover slip.