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. Still the idea of the carbonic acid exhaled by the lungs, being made up of the union of the carbon exhaled with the oxygen taken in, continued to be very extensively entertained. We can only say that to us it seems entirely a child of the imagination; what Horace calls "Mentis gratissimus error;" and shows not only how few people can find leisure to investigate, but how few venture to observe or think for themselves. Abernethy also experimented by holding his hand in carbonic acid, when he found that in about nine hours, three ounces, by measure, of carbonic acid were absorbed by the skin; and in the remaining gas, a considerable quantity of other gas which had been given off, which appeared to be nitrogen. Desirous of ascertaining the quantity of carbonic acid gas given off by his hand, in different gases in a single hour, he introduced his hand into various gases. In the experiment with Drs. Nitrous oxide, there came off 6 Hydrogen 4 Atmospheric air 3