_e._ Though the results of these experiments were not so conclusive as could be wished; yet, comparing them with those of the experiments in section III. it seemed reasonable to conclude, that the production of nitrogene was increased, in proportion as the blood became more fully impregnated with nitrous oxide. From this conclusion, compared with the phænomenon noticed in section 2, and in Div. I. section 4, I am induced to believe that the production of nitrogene during the respiration of nitrous oxide, is not owing to the decomposition of part of the nitrous oxide, in the aëriform state _immediately_ by the attraction of the red particles of venous blood for its oxygene; but that it is rather owing to a new arrangement produced in the principles of the impregnated blood, during circulation; from which, becoming supersaturated with nitrogene, it gives it out through the moist coats of the vessels. For if any portion of nitrous oxide were decomposed immediately by the red particles of the blood, one should conjecture, that the quantity of nitrogene produced, ought to be greater during the first inspirations, before these particles became fully combined with condensed oxygene. If on the contrary, the whole of the nitrogene and oxygene of the nitrous oxide were both combined with the blood, and carried through the pulmonary veins and left chamber of the heart to the arteries; then, supposing the oxygene chiefly expended in living action, whilst the nitrogene was only partially consumed in new combinations, it would follow, that the venous blood of animals made to breathe nitrous oxide, hyper-saturated with nitrogene, must be different from common venous blood; and this we have reason to believe from the phænomena in Div. I. section 4, is actually the case. _f._ Besides the nitrogene generated during the respiration of nitrous oxide, we have noticed the evolution of other products, carbonic acid,[199] and water. [199] The oxygene as we have before noticed, most probably wholly existed in the residual gas. Now as nearly equal quantities of carbonic acid are produced, whether hydrogene or nitrous oxide is respired, provided the process is carried on for the same time; there is every reason to believe, as we have said before, that no part of the carbonic acid produced, is generated from the immediate decomposition of nitrous oxide by carbon existing in the blood. Consequently, in these experiments, it must be either evolved from the venous blood; or formed, by the slow combination of the oxygene of the residual air of respiration with the charcoal of the blood. But if it was produced by the decomposition of residual atmospheric air, it would follow, that its volume must be much less than that of the oxygene of the residual air, which had disappeared; for some of this oxygene must have been _absorbed_ by the blood, and during the conversion of oxygene into carbonic acid by charcoal, a slight diminution of volume is produced.