BREATHING 291 



but to remains of food, decaying teeth, and degenerating 

 tissue about the tonsils and pharynx. 



Ideals of Ventilation. This is a subject which may 

 be touched upon here. We all recognize that rooms 

 in which the air is not freely changed become " stuffy" 

 and depressing to work in. Just what constitutes "bad 

 air" as noticed in such situations has been differently 

 interpreted by writers of different periods. The simple 

 idea that air in close rooms lacks oxygen or is over- 

 charged with carbon dioxid cannot be maintained. 

 The existence in it of volatile poisons is, as we have said, 

 hard to establish. An odor may have a considerable 

 effect upon the human nervous system and it is to be 

 noted that odors in ill-ventilated places are not due 

 simply to the breath but proceed from skins, clothing, 

 lights, and many other sources. 



According to the opinion now generally held the chief 

 trouble with an atmosphere that is regarded as stuffy 

 or close is that it is overheating to the skin. The sur- 

 face of the human body is kept comfortably cool under 

 favorable conditions by the air currents which pass over 

 it and by the evaporation of perspiration. The former 

 are an aid to the latter. In a confined space there is a 

 lack of movement in the air and it tends also to become 

 warm and humid. Moisture is not taken promptly 

 from the skin and its temperature rises. A vasomotor 

 reflex is encouraged by which the cutaneous vessels are 

 dilated and, with the increased blood-flow, the unpleasant 

 warmth is made more pronounced. There is likely to 

 be some reduction of the general blood-pressure, leading 

 to drowsiness or, at least, a feeling of inertia. 



If these views are correct, the most effective precau- 

 tions that can be taken to secure comfort in a room are 

 to keep it cool and to have some circulation of the air. 

 Our fear of strong drafts may be a wholesome one but 

 we should also avoid stagnation. It has been shown 

 that starting an electric fan in a close room may relieve 

 an almost intolerable condition. It does not improve 



