Another system for admitting fresh air into a room, free from fog and other impurities, is that recommended by the Sanitary Engineering and Ventilating Co., 115, Victoria Street, Westminster. They provide for the introduction of fresh air in vertical currents by means of a suitable number and disposition of vertical tubes, varying in size, section, and weight according to each special case. The current can be regulated in amount by throttle valves, and the heated or vitiated air is removed by means of exhaust ventilators, placed directly over the roof or in connection with air flues and shafts. The exhaust ventilator is thus described by the makers: There are no working parts to get out of order, and no attention is required to ensure its constant action. In this respect, a great improvement is claimed over the numerous forms of revolving cowls, which require occasional lubrication, otherwise the working parts become corroded and the cowl ceases to act. They are made of circular or rectangular section, or other shapes to suit special circumstances. One great merit of the system is the element of length which is introduced by means of the tube arrangement, and thus a current is continually passing which diffuses itself over the room. The system admits of a patent air-cleansing box being built into the wall at the foot of the tube, fitted with special deflector plates and a tray to hold water or, when necessary, disinfectants. When the arrangements of furniture or fittings in a room preclude the use of vertical tubes fixed near the ground, they recommend the substitution of a ventilating bracket fixed at 6-7 ft. above the floor. This bracket may contain an air purifying or cleansing box; if required, a valve is provided for regulating the admission of fresh air, and a 9 in. by 6 in. hinged air grating to cover the opening outside. The air-cleansing box is illustrated in Fig. 28: _a_, inside of room; _b_, floor; _c_, trough or tray for holding water or disinfectant fluid; _d_, tube. [Illustration: 28. Sanitary Ventilating Company’s Ventilator.]