To prevent the transmission of heat to other apartments of the house, the precautions hereinbefore mentioned must be observed. Hollow walls must be provided round the heated chambers, to prevent loss of heat on the external side, and the transmission of heat through internal walls. The floors above and below should--if not of solid fireproof construction--be formed as described in the section dealing with the design of the sudorific chambers, with puggings of slag-wool, asbestos, sawdust, or materials having similar properties. Windows should be double. Wherever possible, concrete floors should be provided to the hot rooms and washing rooms, so that they may be covered with tiles or mosaics, and on account of the spilling of water. It should be needless to point out the necessity of having most careful regard to safety from fire by the stoves or furnaces. The ventilation of private baths should receive as much careful attention as those for public use. The hollow external walls may often be used with advantage for the extraction of the vitiated air, which must be let into the cavity at the floor level. If the bath be constructed on the ground floor, with nothing beneath, the system of carrying off the vitiated air by horizontal conduits--recommended for public baths--should be employed, as in the accompanying design for a large private bath, where the whole of the foul air is drawn into one vertical shaft of sufficiently wide section. Much that I have said on the heating and ventilation, and, indeed, on many matters in connection with the design of public baths, applies in the case of the private one, and the reader is therefore referred to preceding pages for many hints as to its construction.