319 
that, by multiplying the time consumed in the experi- 
ment by the number of natural respirations in a 
minute, and dividing the whole bulk of air by the 
product, we obtain the true bulk of air received into 
the lungs in each natural inspiration ; thus, 1 i x 19 
= 209 and V^V = 16.5 cubic inches, which is the 
quantity of air this person naturally inspires *. 
618. It is evident, however, that the respira- 
tion of air, under the circumstances of this experi- 
ment, can with no kind of propriety be considered 
as a just measure of the quantity naturally inspired ; 
for not only do the efforts of the mind, and the opera- 
tions of the apparatus, interfere greatly with the na- 
tural actions of the respiratory organs, but the gross 
quantity of air received in 58 preternatural inspirations, 
can never with justice be assumed as a true measure 
of the quantity breathed in 209 natural respirations. 
On this part of the subject, we continue to think the 
experiments of Dr Menzies (85.) the most unex- 
ceptionable of any which have yet been made, al- 
though the quantity of 40 cubic inches, which he 
assigns, does appear somewhat large. 
619. In their experiments on oxygen, Messrs 
Allen and Pepys found, that a larger quantity of carbo- 
nic acid was formed when that gas was respired than 
when common air was breathed, being, in the former 
case, upwards of 37 cubic inches per minute f? and 
in the latter only 27. This result is directly opposed 
to those obtained by Mr Davy (128.), and is not, in 
* Phil. Trans, an. 1808, p. 
t Phil. Trans. JSO, p. 267. 
