4. Air acts as a powerful stimulus upon the system, through the medium of the lungs. The component parts of this fluid, and its decomposition in the lungs, will be considered in another place[91]. I shall only remark here, that the circulation of the blood has been ascribed, by Dr. Goodwin, exclusively to the action of air upon the lungs and heart. Does the external air act upon any other part of the body besides those which have been mentioned? It is probable it does, and that we lose our sensation and consciousness of it by habit. It is certain children cry, for the most part, as soon as they come into the world. May not this be the effect of the sudden impression of air upon the tender surface of their bodies? And may not the red colour of their skins be occasioned by an irritation excited on them by the stimulus of the air? It is certain it acts powerfully upon denudated animal fibres; for who has not observed a sore, and even the skin when deprived of its cuticle, to be affected, when long exposed to the air, with pain and inflammation? The stimulus of air, in promoting the natural actions of the alimentary canal, cannot be doubted. A certain portion of it seems to be necessarily present in the bowels in a healthy state. [91] It is probable, the first impulse of life was imparted to the body of Adam by the decomposition of air in his lungs. I infer this from the account given by Moses of his creation, in Genesis, chap. ii. v. 7. "And the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life," in consequence of which, the verse adds, he became "a living soul." This explanation of the origin of life in the father of the human race, appears to accord more with reason, as well as the order of the words which describe it, than the common opinion of his having been animated by the infusion of a living soul into his body. 5. Heat is a uniform and active stimulus in promoting life. It is derived, in certain seasons and countries, in part from the sun; but its principal source is from the lungs, in which it appears to be generated by the decomposition of pure air, and from whence it is conveyed, by means of the circulation, to every part of the body. The extensive influence of heat upon animal life, is evident from its decay and suspension during the winter in certain animals, and from its revival upon the approach and action of the vernal sun. It is true, life is diminished much less in man, from the distance and absence of the sun, than in other animals; but this must be ascribed to his possessing reason in so high a degree, as to enable him to supply the abstraction of heat, by the action of other stimuli upon his system.