668 PHYSIOLOGY OF RESPIRATION. 



Some observers (Hermann, Haldane, and Smith) have made 

 careful experiments upon men which also seem to throw much 

 doubt upon the existence of a toxic substance in expired air. In- 

 dividuals kept in a confined space for a number of hours show no evil 

 effects except when the accumulation of the carbon dioxid has 

 reached a concentration of over 4 per cent. At this concentration 

 rapid breathing is apparent, and if it rises to 10 per cent, great 

 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 only when this gas accumulates 

 to a percentage such as is not found in the worst ventilated rooms. 

 As opposed to these negative results, Weichardt reports a series 

 of experiments upon mice in which the expired air of a number of 

 animals was passed through acidulated water, and the latter was 

 then condensed in a vacuum to a small volume and neutralized. 

 When injected into a fresh animal this material brought on a 

 soporific condition, fall of body temperature, and diminution in 

 output of carbon dioxid. The author explains these results on 

 the assumption that some of the so-called fatigue-toxin (keno- 

 toxin) is excreted by way of the lungs, and he believes that the 

 known depressing effects of poor ventilation are an expression of 

 the action of this substance. His results have not been con- 

 firmed and, at present, the definitely known evil results of breath- 

 ing the air of crowded, poorly ventilated rooms must be referred 

 to other possible causes, such as the increase in temperature 

 and moisture. These two conditions cause depression and malaise 

 even when an adequate supply of air is provided. It is possible, 

 also, that the material given off from the skin in the perspiration, 

 sebaceous secretions, etc., may account sufficiently for the odor 

 and, possibly, 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 respiratory movements and the general condi- 

 tion, 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. 



