Analogical evidences were not in favour of the hypothesis of decomposition. It was difficult to suppose that a body requiring the temperature of ignition for its decomposition by the most inflammable bodies, should be partially absorbed and partially decompounded at 98°, by a fluid apparently possessed of uniform attractions. It was more easy to believe, that from the immense quantity of nitrogene taken into the blood in nitrous oxide; the system soon became overcharged with this principle, which not being wholly expended in new combinations during living action, was liberated in the aëriform state by the exhalents, or through the moist coats of the veins. Now if the last rationale were true, it would follow, that the quantity of nitrogene produced in respiration, ought to be increased in proportion as a greater quantity of nitrous oxide entered into combination with the blood. _d._ To ascertain whether this was the case, I made after full voluntary exhaustion of my lungs, one full voluntary inspiration and expiration of 108 cubic inches of nitrous oxide. After this, it filled a space nearly equal to 99 cubic inches. The quantities of carbonic acid and oxygene in these were not determined; but by the test of absorption by water, they appeared to contain only 18 nitrogene; which is very little more than should have been given from the residual gas of the lungs. In a second experiment, I made two respirations of 108 cubic inches of nitrous oxide nearly pure. The diminution was to 95. On analysing these 95, I found to my great surprise, that they contained only 17 nitrogene. Hence, I could not but suspect some source of error in the process. I now introduced into a strong new silk bag, the sides of which were in perfect contact, about 8 quarts of nitrous oxide. From the mode of introduction, this nitrous oxide must have been mingled with a little common air, not however sufficient to disturb the results. I then adapted a cork cemented to a long curved tube to my right nostril; the tube was made to communicate with the water apparatus; and the left nostril being accurately closed, and the mouth-piece of the silk bag tightly adapted to the lips, I made a full expiration of the common air of my lungs, inspired nitrous oxide from the bag, and by carefully closing the mouth-piece with my tongue, expired it through the curved tube into the water apparatus. In this way, I made nine respirations of nitrous oxide. The expired gas of the first respiration was not preserved; but part of the gas of the second, third, fifth, seventh and ninth, were caught in seperate graduated cylinders. The second, analised by absorption, consisted of about 29 absorbable gas, which must have been chiefly nitrous oxide; and 17 unabsorbable gas, which must have been chiefly nitrogene; and the third of 22 absorbable gas, and 8 unabsorbable. The fifth was composed of 27 to 6; the seventh of 23 to 7, and the ninth of 26 to 11.