His object seems to have been as follows: Fontana (a celebrated physiologist, born in the Tyrol about 1734) had showed that a muscle which could no longer be excited to contract under water, might be excited anew, if taken out of the water, and exposed for some time to air. This observation had suggested the idea that air was in some way or other conducive to this "irritability," as it was termed. Dr. Girtanner had also endeavoured to prove that the irritability depended on the oxygen taken into the blood during respiration; and further, that it was in a direct ratio to the quantity of oxygen respired—"an opinion which some writers in this country seem disposed to adopt." Abernethy doubted the soundness of such a view, and he accordingly instituted some experiments, in the hope that if he could not absolutely determine the question, he might throw some light on it. His experiments were very numerous, but he published only a few of them. We will give one or two. "_Having killed a frog_ (for he properly objected to experiments on _living_ animals), he experimented on the muscles of two legs; one was put into a bottle containing oxygen gas procured from manganese, and which was very pure; the other into a bottle containing atmospheric air; the quantity in each bottle was about six ounces by measure; the limbs were supported in the gases, and wholly surrounded by them. After five hours, the muscles had nearly ceased to act in both limbs; those, however, of the thigh belonging to that limb inclosed in the _common air_ acted more vividly than the others, but in a little time even these could no longer be excited. Upon comparing the limbs afterwards, the muscles of that limb which had been exposed to the oxygen gas were evidently the most flabby. Several other trials were made with a similar result;" whence he observes: "I am disposed to conclude that oxygenous gas has _no greater power_ of supporting the irritability of parts _separated_ from the animal than the common atmosphere." In some of his experiments the limbs continued to be excitable after eighteen hours, but with little difference in the two gases. He next made several experiments, by placing the limbs of frogs in _nitrogen_ and _hydrogen_: the limbs in nitrogen lost their irritability in about _two hours and a half_; those in hydrogen, in about _four_ hours. Experiments then follow which consisted in placing other limbs in carbonic acid and nitrous gases respectively; when he found that in both cases the muscles ceased to act in an hour and a half. He also placed limbs in carburetted hydrogen, and found that they ceased to act after the same period. In other experiments, he found the correctness of Fontana's results; viz. that limbs placed under water, and which had lost their irritability, had for a time recovered it by exposure to air and moisture.