18 ORGANISM AND ENVIRONMENT 



Some of the immediate practical applications of the 

 new knowledge with regard to the regulation of 

 breathing are perhaps of sufficient interest to be men- 

 tioned shortly. The air of all sorts of confined spaces 

 is apt to be vitiated by the presence of CO 2 ; and along 

 with the excess of CO 2 there is usually a deficiency of 

 oxygen, since the vitiation is due to processes of oxi- 

 dation, in which oxygen is used up in proportion as 

 CO 2 is formed. In the air of ordinary rooms CO 2 

 is formed and oxygen used up by respiration and by 

 the burning of illuminants. The natural ventilation 

 of an ordinary room is, however, so considerable that 

 it is very seldom that the percentage of CO 2 in the 

 air exceeds 0.5 per cent. What effects will the gaseous 

 impurity in such air have? Clearly none that are 

 appreciable. The breathing will be very slightly 

 deeper, so as to keep the alveolar CO 2 percentage con- 

 stant ; but the increase in breathing will be less than a 

 tenth, and such an increase is totally unappreciable 

 subjectively. The slightly increased breathing will 

 also keep the oxygen percentage in the alveolar air 

 from falling, so that the diminished oxygen percent- 

 age in the air will be of no account. We must thus 

 seek elsewhere than in the gaseous impurities of the 

 air of rooms for the causes of the discomfort felt in 

 crowded rooms. 



In mines and other underground spaces the propor- 

 tion of CO 2 often goes much higher, and may reach 

 about 3 per cent in places where a light will still burn. 

 With 3 per cent of CO 2 in the air the breathing is 

 doubled. This effect becomes just noticeable during 



