To test this matter, Mr. Abernethy confined his hand and arm in various gases containing _no oxygen_—as hydrogen, and then in nitrogen; but he found the carbonic acid gas _still given_ off as before. He then placed his hand in a gas (nitrous oxide) _containing_ oxygen; and lastly, in oxygen itself, to see if it _increased_, or otherwise affected the elimination of carbonic acid; but in neither of those experiments was the carbonic acid thrown off, _increased_, or in any way affected by it.
In a subsequent part of the paper, he remarks on the idea that physiologists entertained of the carbonic acid given off by the lungs being made by the oxygen inspired; but he says, very justly, that the quantity of oxygen is too small for the formation of so much carbonic acid gas as we find given out by those bodies; and that his experiments on the skin clearly prove that the exhaling vessels of the skin emit carbonic acid in a state of _complete formation_; and then adds, what it is difficult to estimate the merits of, without recollecting that it was said half a century ago (and before the experiments of Edwards), "and, doubtless, those of the lungs perform a similar office."
This is one of those bold, and, we believe, successful reasonings from analogy which were very characteristic of Abernethy. The truth is, that even the experiments of Edwards, some of which were, a long time since, repeated by ourselves, with the same results, are not, I conceive, so conclusive as the analogy of Abernethy. It is true, they consisted of placing frogs and other animals in gases not containing oxygen, when it was found, notwithstanding, that there was _no_ diminution in the quantity of the carbonic acid produced, and which therefore could not have been compounded of any oxygen in the gas. But even here many possible sources of fallacy suggest themselves. The previous expulsion _of all_ the oxygen from the animal is obviously a matter of uncertainty. There are, besides, those sources of fallacy which are inseparable in some form or other from all experiments on animals which disturb their natural habits, especially when these disturbances are so great as to amount to suffering. From all such experiments Abernethy _instinctively_ shrunk. His repulsion to them seems not to have rendered it necessary to him to have shown that they were as _physiologically inconclusive_ as they were morally questionable. At all events, his present experiments were not obscured by any such sources of fallacy.