82 



HUMAN BIOLOGY 



About half a pint of water is given off through the lungs 

 in a day. Minute quantities of injurious animal matter 

 are also given off in the breath from even the soundest 

 person. The air leaves the lungs warmer, damper, and with 

 more carbon dioxid than when it entered (Exps. 3 to 9). 



Persons with decayed teeth, catarrh, indigestion, diseased lungs, or 

 other unsoundness give off still more of this material. When many 

 people are assembled in a badly ventilated room, the amount of injurious 

 animal matter in the air is much increased, and is called " crowd poison." 

 Its odor is strong and repulsive to one who just enters the room, but 

 the sense of smell becomes dull to it in a few minutes. It would seem 

 that nature gives a fair warning against harm ; but if we disregard the 

 warning it soon ceases. 



People who are really Unclean. Nature's plan seems to be for us to 

 live out of doors. Air once breathed is impure. It is just as unfit to 

 enter our bodies as muddy water or decayed food. Yet many who call 



themselves cleanly 

 and refined, and 

 will not allow a 

 speck of dirt to 

 remain on their 

 clothes, nor use a 

 spoon just used by 

 another, do not 

 object to breathing 

 into their lungs, 

 over and over 

 again, the cast-off 

 air from the lungs of others. If a window is opened for ventilation, 

 they are horror-stricken for fear of drafts. Drafts are injurious only to 

 persons perspiring, or to those who have coddled the skin by continu- 

 ally overheating it. There are thousands of schools, churches, and 

 theaters all over the land which reek daily with the malodorous particles 

 from the lungs of their occupants. Although the air in them is odorless 

 to those who occupy them, it is disgusting to any one who enters from 

 the fresh air. Figure 80 shows the correct ventilation of a stove-heated 

 schoolroom. 



Dust causes catarrh of the bronchial tubes and chronic 



1 From Coleman's Elements of Physiology (400 pp.). The Macmillan Co., N.Y. 



FIG. 80. VENTILATION OF STOVE-HEATED ROOM. 1 



How are the inlet and outlet situated with reference to the stove ? 



