92 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



Such air can be borne for hours without any evidence of bodily or 

 mental depression. At 8o° F. with moderate humidity, or yo° to 

 75° F. with high humidity, almost all persons begin to show depres- 

 sion, headache, dizziness, and a tendency to nausea. School children 

 and cases of emphysema react least and those with heart troubles 

 most. The subjective symptoms appear when the surface tempera- 

 ture reaches a certain height, for example, 93 ° to 95 ° F. on the 

 forehead (89.5 to 91. 5 F. in cases of heart disease), and the rela- 

 tive moisture of the layer of air in contact with the skin increases 

 20 to 30 per cent (Ercklentz). Under these conditions the normal 

 loss of body heat is interfered with and symptoms appear which are 

 similar in every way to those produced in stuffy, crowded rooms. 



When those within the chamber are allowed to breathe from out- 

 side fresh air raised to the same temperature and degree of humidity, 

 they experience no relief. When those outside the chamber breathe 

 the impure air from within they experience no discomfort. The 

 suffering of those inside the chamber can be immediately relieved 

 by rapidly moving, cooling, or drying the air — mechanical means 

 which enable the body to throw off its heat. On suddenly raising the 

 percentage of C0 2 within the chamber the symptoms are not made 

 worse, while on cooling the air relief is immediately felt. 



Heat stagnation is therefore the one and only cause of the dis- 

 comfort, and all the symptoms arising in the so-called vitiated atmos- 

 phere of crowded rooms are dependent on heat stagnation. The 

 moisture, stillness, and warmth of the atmosphere are responsible 

 for all the effects, and all the efforts of the heating and ventilating 

 engineer should therefore be directed toward cooling the air in 

 crowded places and cooling the bodies of the people by setting the 

 air in motion by means of fans. The strain on the heat-regulating 

 mechanism tells on the heart. The pulse is accelerated, the blood 

 is sent in increased volume to the skin and circulates there in far 

 greater volume, while we must assume that less goes through the 

 viscera and brain. As the surface temperature rises, the cutaneous 

 vessels dilate, the veins become filled, the arteries may become small 

 in volume and the blood-pressure low, and the heart is fatigued by 

 the extra work thrown upon it. The influence of the heat stagna- 

 tion is shown by the great acceleration of the pulse when work is 

 done and the slower rate at which the pulse returns to its former 

 rate on resting. 



The increased percentage of carbonic acid and the diminution of 

 oxygen which have been found to exist in badly ventilated churches, 



