In the experiments when nitrous oxide and hydrogene were respired for about half a minute, the medium quantity of carbonic acid produced, was 5,6 cubic inches nearly. Now we will assume, that the quantity of carbonic acid produced, is in the ratio of the oxygene diminished; and there is every reason to believe, that in the expiration of atmospheric air, the expired air and the residual air are nearly of the same composition. Hence, no more carbonic acid can remain in the lungs or be produced from the residual gas after the compleat expiration of common air, than that which can be generated from a volume of atmospheric air equal to the residual gas of the lungs. The residual gas of the lungs, after compleat expiration, equals at 55°, 32 cubic inches, and 32 cubic inches of common air contain 8.6 cubic inches of oxygene. But in the experiments on the respiration of hydrogene, not only 5.6 cubic inches of carbonic acid were produced, but more than 4 of residual oxygene remained unabsorbed. Hence it appears impossible that all the carbonic acid evolved from the lungs during the respiration of nitrous oxide or hydrogene could have been produced by the combination of charcoal in the venous blood with residual atmospheric oxygene: there is consequently every reason to believe that it is wholly or partially liberated from the venous blood through the moist coats of the vessels. _g._ The water carried out of the lungs in solution by the expired gas of nitrous oxide, could neither have been wholly or partially formed by the decomposition of nitrous oxide. The coats of the vessels in the lungs, and indeed in the whole internal surface of the body, are always covered with moisture, and the solution of part of this moisture by the inspired heated gas, and its deposition by the expired gas, are sufficient causes for the appearance of the phænomenon. There are no reasons for supposing that any of the residual atmospheric oxygene is immediately combined with fixed or nascent hydrogene, or hydrocarbonate, in the venous blood at 98°, by slow combustion, and consequently none for supposing that water is immediately formed in respiration. The evolution of water from the vessels in the lungs, is almost certain from numerous analogies.