_e._ To ascertain the changes effected in a given quantity of atmospheric air by continued respirations, I breathed after a compleat expiration, at temperature 63°, 161 cubic inches of air for near a minute, making in this time, 19 deep inspirations. After the compleat expiration, which was very carefully made, the gas filled a space nearly equal to 152 cubic inches, so that 9 cubic inches of gas had disappeared. The 152 cubic inches analised, were found to consist of cub. in. Nitrogene 111,6 Oxygene 23, Carbonic acid, 17,4 The 161 cubic inches before inspiration, were composed of cub. in. Nitrogene 117,0 Oxygene 42,4 Carbonic acid 1,6 But the residual gas in the lungs before the experiment, was of different composition from that remaining in the lungs after the experiment. Making corrections on account of this circumstance, as in section IV. it appears that about 5,1 of nitrogene were absorbed in respiration, 23,9 of oxygene consumed, and 12 of carbonic acid produced. I repeated this experiment three times; in each experiment the diminution after respiration, was nearly the same; and the residual gas making the necessary allowances, of similar composition. So that supposing the existence of no source of error in the experiments from which the quantity and composition of the residual gas of the lungs were estimated in section IV. the absorption of nitrogene by the venous blood, appears almost demonstrated. _f._ To compare the changes effected in atmospheric air by respiration of the smaller quadrupeds, with those in the experiments just detailed, I introduced into a jar of the capacity of 20 cubic inches filled with mercury in the mercurial trough, 15 cubic inches of atmospheric air which had been deprived of its carbonic acid by long exposure, to solution of potash. Temperature being 64°, a healthy small mouse was quickly passed under the mercury into the jar, and suffered to rest on a very thin bit of cheese, which was admitted immediately after. He continued for near 40 minutes without apparently suffering, occasionally raising himself on his hind legs. At the end of 50 minutes, he was lying on his side, and in 55 minutes was apparently dying. He was now carefully taken out through the mercury by the tail, and exposed before the fire, where he soon recovered. After the cheese had been carefully removed, the gas in the jar filled a space nearly equal to 14 cubic inches; so that a diminution of a cubic inch had taken place. These 14 cubic inches analised, were found to consist of cub. in. Carbonic acid 2,0 Oxygene 1,4 Nitrogene 10,6 The 15 cubic inches before the experiment, consisted of cub. in. Oxygene 4 Nitrogene 11