A circular tissue recording chamber has a cavity therein for retaining tissue or cell samples immersed in a liquid bath. The temperature of the bath is maintained at a selected level by a transparent heater positioned beneath the bath, wherein the heater is comprised of a grid of fine wires supported on a transparent mylar substrate. Liquid is introduced into the bath through a serpentine passageway also in proximity with the heater, whereby the temperature of the liquid is raised to that of the bath as it traverses the passageway. The recording chamber has a thickness of approximately 1 cm so as to be readily usable with a high magnification microscope.
