616 PHYSIOLOGY OF RESPIRATION. 



distress is felt and the face becomes congested and blue. These 

 authors conclude that expired air is injurious in itself only from the 

 carbon dioxid it contains, and not because of any special poison. 

 We must admit, therefore, that the existence of an organic poison 

 in the expired air has not been conclusively demonstrated in fact, 

 has been made exceedingly improbable. The definitely known evil 

 results of breathing the air of crowded, poorly ventilated rooms must 

 be referred to other possible causes, such as the increase in temper- 

 ature and moisture. These two conditions cause depression and 

 malaise even when good ventilation is provided. It is possible, also, 

 that the material given off from the skin in the perspiration, seba- 

 ceous secretions, etc., may account sufficiently for the odor and pos- 

 sibly also for some of the general evil effects. If the ventilation is so 

 poor that the carbon dioxid accumulates to the extent of 3 to 4 per 

 cent., then this factor begins to exercise a direct effect upon the res- 

 piratory movements and the general condition, an effect which 

 increases as the percentage of carbon dioxid rises. 



Ventilation. It is obvious from the foregoing statements that 

 our knowledge is not yet sufficiently complete to enable us to say 

 positively at what point air in a room becomes injurious to breathe, 

 whether from products of expiration, or exhalation, or changes in 

 temperature and moisture. The statement is frequently 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 the ex- 

 periments of Haldane and Smith seem to disprove this statement 

 entirely. The practical rule 'in ventilation is to keep the air in 

 chambers as nearly as possible of the composition of the atmosphere 

 outside. Since carbon dioxid is the constituent of the air that is 

 most easily determined the relative purity of room air is judged 

 conveniently by quantitative estimations of this constituent. Or- 

 dinary atmospheric air contains, on the average, 0.04 per cent, 

 of carbon dioxid that is, 4 parts to 10,000. The hygienists main- 

 tain that the ventilation should be sufficiently ample to keep the 

 carbon dioxid down to 6 parts per 10,000, thus leaving 2 parts 

 per 10,000, 0.02 vol. per cent., as the permissible limit of vitia- 

 tion by breathing. To determine on this basis the amount of 

 air necessary for each person the following formula is used: 

 d == l y in which d represents in liters the delivery of fresh air per 

 hour; e, the amount of CO 2 expired per hour in liters; and r the 

 ratio of permissible vitiation of the air by CO 2 . Assuming this 

 latter factor, in accordance with the above statement, to be equal 

 to 0.02 per cent., and e to be equal to 20 liters per hour (500 X 

 0.04 X 17 X 60), the value of d is equal to 100,000 liters of air 

 per hour for each person. The rapidity of renewal of air will 

 depend naturally upon the cubic space allotted to each individ- 



