THE LUNGS AND RESPIRATION. 215 



breath of persons is tainted more or* less strongly with ob- 

 jectionable odors, which in many cases are not necessarily 

 due to a careless condition of the teeth, but due to sub- 

 stances either volatile, or to small particles of disintegrated 

 tissue which have emanated from the lungs. Our bodies 

 seem peculiarly susceptible to such eliminated particles, and 

 an atmosphere that has been vitiated even to a small extent 

 with them becomes at once unpleasant to our nostrils, and 

 if in spite of this warning we persist in breathing it, there 

 results finally a dullness, a headache, or a general indisposi- 

 tion which, if continued from day to day, surely and inevit- 

 ably leads to an undermining of the general health and 

 energies, and may succeed in cutting the life unnaturally 

 short. 



There are persons who seem to think that the import- 

 ance of ventilation as it is urged* by persons who have 

 studied that subject is somewhat of a scientific fad, and the 

 day is not yet here when persons who have the ventilation 

 of crowded rooms in charge always appreciate the impor- 

 tance of the duty so assigned to them. In determining the 

 amount of air which ought to be admitted into a room, 

 stoves which consume large quantities of oxygen, or gas jets 

 which use up a certain supply of the same gas, must be 

 taken into consideration, for the consumption of oxygen in 

 a stove may, under certain circumstances, be many times 

 that of a single person. Then, further, as there are always 

 emanating from a heated stove certain poisonous gases, the 

 necessity for a more perfect ventilation than ordinary is at 

 once apparent > 



THE CHEMISTRY OF RESPIRATION. 



1. Composition of Inspired and Expired Air. The 

 composition of the air which we inspire is about as follows : 



Nitrogen 79 per cent. 



Oxygen 20 " 



Carbon Dioxide 004 " 



Water in amounts depending on the humidity of the atmosphere. 



