THE CHEMISTRY OF RESPIRATION. 401 



air its volume will be found diminished, since it has lost 5.4 

 volumes per cent of oxygen and gained only 4.3 of carbon 

 dioxide. In round numbers, 100 volumes of dry inspired air 

 at zero, give 99 volumes of dry expired air measured at the 

 same temperature and pressure. 



Ventilation. Since at every breath some oxygen is taken 

 from the air and some carbon dioxide given to it, were the 

 atmosphere around a living man not renewed he would, at 

 last, be unable to get from the air the oxygen he required; he 

 would die of oxygen starvation or be suffocated, as such a 

 mode of death is called, as surely, though not quite so fast, as 

 if he were put under the receiver of an air-pump and all the 

 air around him removed. Hence the necessity of ventilation 

 to supply fresh air in place of that breathed, and clearly the 

 amount of fresh air requisite must be determined by the 

 number of persons collected in a room; the supply which 

 would be ample for one person would be insufficient for two. 

 Moreover fires, gas, and oil lamps, all use up the oxygen of 

 the air and give carbon dioxide to it, and hence calculation 

 must be made for them in arranging for the ventilation of a 

 building in which they are to be employed. 



In order that air be unwholesome to breathe, it is by no 

 means necessary that it have lost so much of its oxygen as to 

 make it difficult for the Body to get what it wants of that 

 gas. The evil results of insufficient air-supply are rarely, if 

 ever, due to that cause even in the worst-ventilated room for, 

 as we shall see hereafter, the blood is able to take what 

 oxygen it wants from air containing comparatively little of 

 that gas. The headache and drowsiness which come on from 

 sitting in a badly ventilated room, and the want of energy 

 and general ill-health which result from permanently living in 

 such, are dependent on a slow poisoning of the Body by the 

 reabsorption of the things eliminated from the lungs in 

 previous expirations. What these are is not accurately 

 known; they doubtless belong to those volatile bodies men- 

 tioned above, as carried off in minute quantities in each 

 breath; since observation shows that the air becomes injuri- 

 ous long before the amount of carbon dioxide in it is suffi- 

 cient to do any harm. Breathing air containing one or two 

 per cent of that gas produced by ordinary chemical methods 

 does no particular injury, but breathing air containing one 

 per cent of it produced by respiration is decidedly injurious, 



