From all that has been said, we may fairly conclude, that no proof can be brought sufficient to prove the existence either of oxygen air or any other species of aerial fluid, in its elastic state, in the blood. Neither can we prove that any part of the condensable part of oxygen air is received by the breath in the lungs. It is, however, probable that this condensable part may be received into the stomach with our food; that having passed through the various channels of circulation, and arrived at last at the surface, it there resumes its aerial nature by combining with the superfluous heat of the body, and is evaporated through the pores of the skin by insensible perspiration. The aerial vapour which passes off by these pores indeed has been discovered to partake of the nature of _fixed air_; but we know that this species of gas always contains the basis of oxygen, being indeed composed of it; and whether the oxygen be taken into the body in its pure state or not, the result would undoubtedly be the same; for an union would be formed between it and the carbonic particles to be thrown off from the body. But thus we can never suppose the basis of oxygen or any other air to be a permanent part of the composition of our bodies; nor can the quantity of it be augmented by breathing any kind of air. The readiest way to increase the quantity seems to be by drinking fermented liquors. Thus, if the body is too hot, the superfluous heat will have a proper subject to act upon, viz. the condensable part of the fixed air; and hence we may perhaps account for the very grateful and cooling sensation produced by drinking these liquors in some diseases. With respect to the existence of _carbon, charcoal_ or _hydrogen_ in the blood, it is probable that it exists in equal quantity at all times, being indeed the fundamental material of the whole body, and probably only a modification of that _dust_ from whence man was originally taken.[74] When the blood therefore grows very black, when the teeth are covered with a black sordes, the hands become foul, &c. we may say, indeed we too surely _feel_, that, in such cases, there is a propensity in the body to return to its original state of dissolution; but there is not one solid reason for supposing the proportion of its materials to be varied; that there is a collection of _oxygen_ in one part, _hydrogen_ in another, or in short that nature can admit of any such disproportion taking place.