224 APPLIED PHYSIOLOGY 



breathed. The heat of a closed room greatly intensifies 

 the effect of the foul air. 



386. Cause of bad effects of foul air. No one thing can 

 be found in stuffy air to account for all the bad feelings which it pro- 

 duces. The diminution of oxygen is too slight to produce noticeable 

 effects, but the combination of heat and foul odors is very oppressive 

 to persons not accustomed to them, while the carbonic acid gas tends 

 to cause drowsiness and dullness of mind. Those who live in a foul 

 atmosphere continually are usually too poor to buy nourishing food, 

 and too busy to take exercise in the open air, and, moreover, are 

 greatly overworked. These causes produce even more ill health than 

 the foul air. 



387. Bad odors. Decaying matter gives off bad odors. Many 

 animals and vegetables have an offensive smell, and in many manu- 

 factures foul odors are continually poured into the air. These odors 

 in the air are seldom harmful, yet the s*ource of the odors is usually 

 dangerous to health, and the odors are given off as a warning. It 

 is nearly always true, that harmful things have an offensive smell and 

 taste. So a bad odor reveals a decaying body which might poison a 

 well, or a disease which might be communicated to others. 



Since odors are only signs, the danger is not past if only the odor 

 is destroyed. Ammonia, carbolic acid, or perfumery may mask the 

 odor, but they only obscure the source of danger. 



388. Sewer gas. Sewer gas is exceptionally offensive 

 and penetrating. The odor is not especially harmful, but 

 disease germs which are emptied into the sewer from sick 

 rooms are easily carried with the gas. Usually the strong 

 odor betrays the leak in the pipes before the germs have 

 gained an entrance. 



389. Cellar air. Cellars are apt to be closed, so that little 

 fresh air and light can enter. Decaying vegetables and other sub- 

 stances may accumulate in the corners. This makes a breeding place 

 for disease germs, which may be carried up through the floors into 

 living rooms above. A cellar should be kept dry, clean, and well 

 aired. 



