I thought of trying to observe whether while I alternately breathed quantities of nitrous oxide and oxygene gas and common air, I could observe any difference in the operation of a blister beginning to bite the skin. It would be of consequence to ascertain the effect of regulating by compression the flow of blood, while stimulants of various kinds (and heated bodies among the rest) were applied to or near the extremities—because in erisipelas and various inflammatory affections, a ready and pleasant cure might be effected by partial compression of the arteries going to the diseased part; and a great improvement in practice thus obtained. But I should run into an endless digression, were I to enumerate possible physiological experiments with artificial airs, or to speculate on the mechanical improvement of medicine, which at present as far as mechanical means of affecting the living system are concerned, is with us in a state that would almost disgrace a nation of savages. IV. CONCLUSION. From the facts detailed in the preceding pages, it appears that the immediate effects of nitrous oxide upon the living system, are analogous to those of diffusible stimuli. Both increase the force of circulation, produce pleasurable feeling, alter the condition of the organs of sensation, and in their most extensive action destroy life. In the mode of operation of nitrous oxide and diffusible stimuli, considerable differences however, exist. Diffusible stimuli act immediately on the muscular and nervous fibre. Nitrous oxide operates upon them only by producing peculiar changes in the composition of the blood. Diffusible stimuli affect that part of the system most powerfully to which they are applied, and act on the whole only by means of its sympathy with that part. Nitrous oxide in combination with the blood, is universal in its application and action. We know very little of the nature of excitement; as however, life depends immediately on certain changes effected in the blood in respiration, and ultimately on the supply of certain nutritive matter by the lymphatics; it is reasonable to conclude, that during the action of simulating substances, from the increased force of circulation, not only more oxygene and perhaps nitrogene must be combined with the blood in respiration,[228] but likewise more fluid nutritive matter supplied to it in circulation.