280 
tending to the natural actions of the respiratory or- 
gans' (92. et seq.), in the conduct of all experiments 
made on the exercise of this function, by shewing, 
that, in all examples of natural respiration, little or 
no variation occurred in the volume of air employ- 
ed, but that, in proportion as these organs suffered 
distress and oppression, the greatest irregularities 
prevailed. 
571. These facts are supported, in all their circum- 
stances, by the results obtained by Messrs Allen and 
Pepys. We have seen (568.), that, when a Guinea 
pig was made to breathe a given quantity of air in a 
natural manner, no variation whatever was observed 
in its bulk ; and even in man, in whom many causes, 
which do not affect the lower animals, contribute to 
produce error, it appears, that, when the respiration 
was nearly natural, the general average of the defi- 
ciency, in the total amount of common air inspired, 
was only about six parts in 1000 (566.); and in 
one instance, it was considerably less than two. " The 
smallness of this deficiency," say these chemists, "sur- 
prised us very much ; and, in our opinion, it prin- 
cipally arises from the difficulty, or," as they else- 
where say, " the imposibility of always bringing the 
lungs to the same state after forcible expiration V 
572. Notwithstanding the justice of this remark, 
they seem, however, entirely to have neglected its 
import in the inference which they have drawn from 
their fourteenth and fifteenth experiments. In the 
first of these experiments, 300 cubic inches of 
* Phil, Trans. JS08, p. 253.?5i C5&. 
