318 
oxygen and carbon in those organs must be much 
facilitated by the more condensed state of that gas, 
instead of being counteracted, as it would necessarily 
be, by the expansion which is generally conceived to 
happen. Without increasing the actual dimensions, 
we may also, by such an hypothesis, be said really 
to augment the capacity of the lungs ; since we com- 
press into the same space a much larger quantity of 
that aeriform fluid which they are destined to receive ; 
and, perhaps, the very different estimates which 
have been given of the capacity of these organs, and 
of the ordinary bulk of air taken in and expelled in 
one respiration, may receive illustration from the 
operation of such a cause. In the ordinary exercise 
of this function, however, this circumstance is not 
discovered, because all the causes operating on the 
air, either mechanically or chemically, preserve, as 
it were, an equilibrium of action, and, therefore, 
neither excess nor deficiency any where prevails ; but 
when this equilibrium is disturbed by causes which 
induce a preternatural state of those organs, and 
change the usual relations which they maintain with 
the atmosphere, then the circumstance of this com- 
pressed state of the air becomes apparent. 
617. Messrs Allen and Pepys farther endeavoured 
to determine, by their experiments, the quantity of 
air received into the lungs in an ordinary inspiration. 
In these experiments, a person in eleven minutes 
passed 3460 cubic inches of atmospheric air through 
his lungs, in which time he made about 58 respira- 
tions. And as, on ordinary occasions, this same per- 
son breathed 19 times in a minute, it is inferred, 
