The next discovery of importance on respiration, is that by Dr.
Black, who observed the formation of carbonic acid. Succeeding la-
bourers in the same field of inquiry, it is observed, are too numerous
for justice to be done to every one; and the principal information
collected from them relates to measures of quantity. Dr. Goodwin
estimated the residual gas in the lungs, after expiration, at 109 inches.
Dr. Menzies found the absorption of oxygen nearly 52,000 inches in
twenty-four hours.
Lavoisier and Seguin, from a series of elaborate experiments, con- cluded that more oxygen was absorbed than evolved, as carbonic acid, and thence imagined that water was formed by the union of oxygen and hydrogen in the lungs.
Their experiments showed the consumption of oxygen to be greater in a colder atmosphere, and to be increased also during digestion and during exercise ; and they estimated the average consumption at 41,000 inches per day.
The quantity of carbonic acid formed, was first estimated by Mr. Davy.
The authors conceiving that many important points are not yet satisfactorily settled, undertake to examine in the present communication,—
1. The average quantity of oxygen converted into carbonic acid in ordinary respiration.
2. Whether oxygen is absorbed by the blood.
3. Whether azote is absorbed, and whether hydrogen or other gas is evolved.
On account of the impossibility of knowing, with precision, the quantity of gas remaining in the lungs after expiration, and the consequent difliculty of deciding whether any gas is absorbed in the act of respiration, it was determined to perform the experiments on such large quantities of air at a time, that the error arising from residual gas might bear a small proportion to the whole quantity.
The apparatus for the first five experiments consisted of two gasometers, one of which contained 4200 inches of atmospheric air over water, from which the inspirations were made, and the other being filled with mercury, was employed to receive the gas after expiration; but as its capacity was only 300 inches, it was necessary for the operator to retain his breath for about fifteen or twenty seconds, till the quantity expired had been read off, noted, and expelled from the gasometer; after which the same process was repeated about twelve times. The quantity of inspired air having now been read off from the water gasometer, the quantity expired was ascertained by casting up the amount of the successive fillings of the mercurial gasometer. From an average of these five experiments, there appeared to be a diminution of Wenty inches in 3700. But the authors are inclined to ascribe this difference to the difficulty above mentioned, of bringing the lungs to the same state of contraction after the experiment as they had been before.
In determining the quality of the expired gas, lime-Water was first
