Spallanzani found that the exposure of cold-blooded animals to the air was attended with exudation of _carbon_, a phenomenon similar to that of respiration. There appears, however, to be some source of error in these experiments, for Spallanzani removed the lungs, and this operation rendered the animal liable to the absorption of air and loss of blood. Dr. Edwards sought to effect the same purpose by a different and more successful measure. He also confined frogs in vessels of atmospheric air, and fastened bladders round the head and neck, tight enough to stop the entrance of air to the lungs. At the expiration of two hours the air was examined in the bladder, and it was found to contain an excess of _carbonic acid_. The same result was obtained from salamanders. It appears, therefore, that while air is in contact with the skin, _carbon_ is given out; but whether this be the effect of exhalation merely, or that _oxygen_ is actually absorbed, and _carbon_ transpired, is a question which led to further inquiries. Dr. Edwards, therefore, inclosed cold-blooded animals in _solid substances_, in order to determine the influence of dark-coloured blood, free of all external agency, in the production of chemical changes, and to observe its sensible effect upon the nervous system. In the year 1779 three toads were confined in a box hermetically sealed, and so deposited in the Academy of Sciences. Eighteen months after, the box was opened, and one toad was found dead. These animals have been found alive in blocks of coal after an imprisonment of some years, and have [p145] also been sealed up during similar periods without perishing. Possibly some hole or crevice might have admitted a little air. But, in Hevissant’s experiment of 79, care seems to have been taken to obviate this suspicion. Dr. Edwards, however, determined to put the question to the test. He enclosed ten out of fifteen frogs in thick wooden boxes, and filled the interstices with plaster, covering them over with the same substance, the toads lying each in a central hole or bed. The other five toads were at the same time submersed in water, and at the expiration of eight hours they were found to be dead. In sixteen hours more, one toad was taken from a box and found to be lively, and was reconsigned to its prison. On the sixteenth day the toads in the boxes were discovered alive, and thus the fact was established that these animals can live far longer in a state of asphyxy confined in solid substances, than when submersed in water. This was confirmed by repeated trials on salamanders, frogs, and toads. The frogs perished quickest. Thus an extraordinary fact is established, as regarding reptiles, since it affords an exception to the general rule that _all animals require a_ CONSTANT _supply of fresh air for the maintenance of their existence_. Similar trials were repeated in sand, and with the same results.