Abstract: Cryogenic apparatus comprises the combination of an insulated Dewar container for cryogenic liquid and a probe-like device for the introduction of heat into the liquid, the device being of elongated form, increasing in cross-section from an upper, heat-input end towards a lower, heat-output end. The device may be of copper and substantially conical whereby its cross-section is substantially circular. The heat-input end of the device has an upper extension which penetrates a low-loss self-venting cover-plug disposed in the neck of the insulated container. A metallic "cold" plate is attached to the upper end of the extension and provides a large-area surface over which cold is distributed by convection.