214 STUDIES IN ADVANCED PHYSIOLOGY. 



than this. These figures ought not to be passed over 

 thoughtlessly, but ought to serve as a criterion in judging 

 whether any room in question is really capable of housing 

 one, or two, or three individuals, as the case may be. 

 Students, especially, are sometimes not overly careful in. 

 crowding two or three into a small room, the capacity of 

 'I which would be but little more than that required for a 

 single occupant. 



Wliat Vitiates Air? 



It was pointed out that in breathing, oxygen is taken 

 from the air and carbon dioxide given to it. But air be- 

 comes vitiated and is no longer fit to be breathed, not be- 

 cause too much of the oxygen has been removed, or because 

 too much carbon dioxide is present in it. In an atmosphere 

 in which the amount of oxygen should be materially reduced 

 the blood could still get all of that gas it would need. An 

 atmosphere containing quantities of carbon dioxide very 

 much greater in proportion than that in the air of badly 

 ventilated rooms, would still be perfectly harmless to 

 breathe. Of course if the oxygen supply should be reduced 

 so much as to make it impossible to get enough of that gas, 

 or if there should be so much carbon dioxide in the atmos- 

 phere that it would almost entirely replace the oxygen, as 

 it is sometimes in deep wells or in mines, then the carbon 

 dioxide would prove injurious and fatal, but not because it 

 itself is injurious or poisonous, but simply because it has 

 displaced the necessary oxygen. 



The thing that makes air which has been breathed once 

 no longer fit for respiration is the fact that such expired air 

 contains organic impurities which have been breathed out 

 from the lungs. It is impossible to determine just what these 

 impurities are, but they are probably volatile substances of a 

 poisonous nature, or may actually be particles of decayed 

 lung or other organic tissue. It is this organic admixture 

 that plays havoc in instances of insufficient ventilation. An 

 idea of the large amount of such organic material breathed 

 out may be gained when we remember how frequently the 



