Pure air is absolutely indispensable for mental work. Much time and energy is wasted by teacher and pupil in trying to work in vitiated atmosphere. The educational results obtained in the school will be influenced more than has been conceded by the character of the air the pupil and teacher are forced to breathe. Vitiated air will produce sluggishness, headache, listlessness, inattention, lack of energy and a depression of mental vigor which will prevent the child from doing his best work. The same influence will be felt by the teacher and the result will be inefficiency in instruction. Natural means of ventilation should not be relied upon since it is difficult to get a sufficient amount of fresh air into the rooms in winter time without creating objectionable drafts which interfere with heating. Regardless of the method employed in ventilating it is a good plan to open all of the doors and windows occasionally during the day and flush the rooms with fresh air. At such time the children should exercise or employ some means to prevent them from taking cold. Schoolhouses should be provided with the combined plenum and vacuum system and operated in conjunction with the heating plant in cold weather. In this way the air that is admitted can be regulated not only as to quantity, but also the velocity can be controlled and likewise the humidity and temperature. Heating The relation between ventilating and heating must be kept in mind. It is not only a question of providing a proper amount of pure air, but also a question of the proper temperature of the air. A poorly ventilated room is always more difficult to heat and an improperly heated room is very difficult to ventilate. Local heating should never be used in a schoolroom except when impossible to provide better means. The best arrangement for heating school buildings is hot water or steam in connection with the ventilating system in which the air is passed over hot radiators before being forced into the classrooms and corridors. This is supplemented by heat from the radiators placed in proper locations throughout the building. In this way the temperature of the room may be kept at the proper degree and at the same time the air circulation and the humidity properly regulated. Best work is accomplished by the children when the temperature is kept at about 68° F. School Desks The furniture most important to the health of the child is the desk and the desk chair. These should be very carefully adjusted to the child; if this is not properly done the child will have a tendency to assume a faulty posture which will favor the development of curvatures of the spine and other physical defects.