Atmospheric Air and Oxygen Gas by Respiration . 259 
Calculation for Carbonic Acid. 
100 : 8 : : 9872 : 789,76. 
So that 789,76 cubic inches of carbonic acid gas were given 
off in 24-I minutes, which gives thirty- two cubic inches per 
minute. But here it must be noticed that the respiration 
was more rapid than in the nth experiment, and a larger 
quantity of carbonic acid given off in the same time. This 
agrees with the 12th experiment. 
We are very much inclined to think that, in ordinary respi- 
ration, a great part of the air is returned unaltered, viz. that 
contained in the fauces, in the trachea, and probably a portion 
of that in the larger branches of the bronchia. If this circum- 
stance be not adverted to in experiments upon small quanti- 
ties of air, the results can never be correct. There is even a 
considerable difference in the quality of the first and last por- 
tions of a single inspiration. In some experiments made with 
a view to this subject, a small quantity of the first portions, 
given off in a common and natural expiration, was received in 
a vessel over mercury ; on examination, it only contained 3.5 
per cent, carbonic acid ; in other experiments the first por- 
tions contain from three to five per cent. ; while the general 
average appears by the 11th, 12th, and 13th experiments, to 
be about eight. 
The operator, after rather more than a natural inspiration, 
expired 204 cubic inches into the mercurial gasometer, making 
his utmost efforts to press as much as possible out of the 
lungs, this contained 9 5 per cent, of arbonic acid. Here we 
are to recollect, that these 204 cubic inches contained the first, 
as well as the last portions ; the first portions have been 
L 1 2 
