FRESH AIR AND EFFICIENCY 281 



exhaled organic matter of human origin, but singly 

 and collectively they failed under the ordeal of experi- 

 mentation to justify this contention, and as our know- 

 ledge of physiology increased they became more and 

 more in conflict with its findings. 



As to CO*. When human beings foul an atmos- 

 phere by respiration they add CO 2 , a trace of organic 

 matter, and a variable amount of odour, and they 

 reduce the oxygen content. As to CO 2 , even under 

 the worst conditions of human fouling, this inert gas 

 does not exceed 0.8 per cent of the atmosphere it 

 seldom exceeds 0.4 per cent and experimentally we 

 find that the only result from breathing air with even 

 i per cent of CO 2 is a very faint increase in the depth 

 of breathing (the slight rise in the CO 2 of the blood 

 decreasing its alkalinity and so exciting the respiratory 

 centre); and we know that in the small air sacs of the 

 lungs the CO 2 is from 5 to 6 per cent. And yet until 

 comparatively recently it was believed that it was the 

 CO 2 added to the air by human respiration that was 

 the responsible factor in the evil effects of foul air. 



As to Oxygen. The oxygen content of the most 

 crowded and worst ventilated room is never I per cent 

 below its amount in the outside air, and therefore it is 

 always higher than it is in the Alpine health resorts ; 

 and the oxygen content of the air in the pulmonary 

 air sacs is quite 20 per cent below that in the external 

 air. The hypotheses of a volatile poison or of a toxic 

 protein (or "crowd poison") in the trace of organic 

 matter in expired air both lack experimental confir- 

 mation. 



As to Odour. In ordinary respiration the expired 

 air is free from suspended matter, and sterile; and 

 the odour of "stuffiness" in a crowded room is de- 

 rived from albuminous decomposition products de- 

 rived from buccal, nasal, and cutaneous surfaces, and 



