Abstract: This invention relates to the freezing of biological tissues in a rapid manner in order to prevent the formation of ice crystals in tissue surface layers. The apparatus consists of a reservoir containing a liquid quenchant near its melting temperature, a jet nozzle for delivery of the liquid, and a means of preventing liquid from contacting tissue until it has reached low temperature and a uniform flow has been established.Fixation occurs within a small fraction of a second near the tissue surface, so that small polar molecules and ions can be prevented from diffusion during and after fixation, and their position at the time of fixation can be later determined. The process is applicable to freeze-fixation, freeze-preservation, freeze-fracture, and to rapid cooling of small areas of surfaces when it is desired to limit crystal formation by establishing a high rate of cooling.