CHANGES IN AIR AND BLOOD IN RESPIRATION. 663 



seen, modern investigations have made this beUef improbable, and 

 have shown that CO2 in expired air in concentrations of 1 per 

 cent, exerts no injurious effect. Under sedentary conditions such 

 as need to be considered usually in problems of ventilation, the 

 important factors to be borne in mind are the temperature, moist- 

 ure, movement, and sweetness of the air. In crowded rooms the 

 exhalations from the body may occasion a disagreeable odor which 

 is offensive, although so far as known not physically injurious. 

 The renewal of air must be adequate to prevent the noticeable 

 accumulation of these volatile products, and if the air is recirculated 

 these substances should be removed by a system of washing. The 

 essential factors to be considered in ventilation are, however, 

 temperature and moisture. When these factors are allowed to 

 increase they soon produce a condition of hstlessness and dis- 

 comfort. The reason for this effect has not been studied with 

 sufficient care, but possibly it is connected with some interference 

 with the body metabolism or with some derangement of the tem- 

 perature-regulating mechanisms of the body. In accordance with 

 this view it is found by experiment, and indeed, it is a matter of 

 e very-day experience, that when the air is kept in movement, by 

 fans, for example, the ill effects of a warm and stuffy room are 

 greatly lessened. The moving air by accelerating the evaporation 

 of the perspiration of the skin increases the loss of heat from the 

 body (see Chapter LI). To ensure physical comfort and mental 

 efficiency the ventilation of crowded rooms must be sufficient to 

 keep the degree of temperature and moisture within certain limits 

 the range of which must be determined by actual experiments. 

 Experiments of this character made in this country indicate that 

 the optimal conditions approximate a temperature of 65° to 70° F, 

 and a relative humidity of 50 to 60 per cent., or, to express this con- 

 dition in another form, the wet-bulb thermometer should indicate 

 a temperature of about 56° F. (E. V. Hill). When new air is taken 

 from the outside, arrangements should be provided to heat and 

 moisten it, or to cool and dry it, according to conditions, and to 

 regulate the flow of air in accordance with the number of persons 

 and the volume of the enclosed space. The amount of cubic space 

 allotted to each individual will vary naturally according to the 

 rate of renewal or movement of the air. The older estimate of 

 30 cubic feet per minute to each person may be reduced with 

 safety to as httle as 15 cubic feet per person, provided the move- 

 ment of air is adequate.* Since the idea of an organic poison in 

 the expired air has been abandoned it has been found feasible to 



* See Larson, "Transactions of American Society of Heating and Ventilat- 

 ing Engineers," 1916, vol. 22, p. 11. 



