CHANGES IN AIR AND BLOOD IN RESPIRATION. 673 



formerly made in the books that, when the air contains as much as 

 1 per cent, of carbon dioxid (Smith) that has been produced by 

 breathing, evil results, as judged by one's feelings, are sure to occur, 

 but this statement was founded on the belief that an organic poison 

 is present in expired air. As we have seen, modern investigations 

 have made this. belief improbable, and have shown that CO 2 in 

 expired air in concentrations of 1 per cent, exerts no injurious effect 

 except possibly under conditions requiring much muscular exertion. 

 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, moisture, 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 pre- 

 vent the noticeable accumulation of these volatile products, and if 

 the air is recirculated these substances should be removed by a sys- 

 tem of washing. The essential factors to be considered in ventila- 

 tion are, however, the temperature and degree of moisture. When 

 these factors are allowed to increase they soon produce a condition 

 of listlessness and discomfort. The reason for this effect has 

 not been studied with sufficient care, but possibly it is connected 

 with some derangement of the temperature-regulating mechanisms 

 of the body. In accordance with this view it is found by experi- 

 ment, and indeed, it is a matter of every-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 in- 

 creases 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 deter- 

 mined 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. When the new air is taken from the outside, arrange- 

 ments 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 accord- 

 ance 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 little as 15 cubic feet per person, 

 provided the movement of air is adequate.* Since the idea of an 



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

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



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