By Voluntary Motion is meant the action of any Muscle or Muscles produc’d by an immediate or conscious determination of the Mind; of this kind are the several occasional motions of the Body. Involuntary or Habitual Motions are such as proceed originally from the Mind also, but are so establish’d, by long custom, that the Mind is not immediately conscious of them, nor can stop them at pleasure[13]. To this class, the Motion of the Heart, the peristaltic Motion of the Stomach and Guts, Respiration, and several Motions of the Eyes belong. The vital Motions are suppos’d to be continued by a stimulus constantly applied to the Fibres of the Muscles which perform them. Hence the Ventricles of the Heart are constantly irritated and stretch’d by the Venous Blood, which brings them into contraction, to propel the Blood through the Body. Thus the Alimentary Tube is mov’d by the irritation of the food, rarefied air, &c. And in like manner respiration is carried on, by the uneasiness that is felt in the Lungs at the end of every dilatation and contraction of the Thorax, which is owing to the resistance that the Blood meets with, both from the collapsing of the Lungs, and from the pressure of the rarefied air on the small Pulmonary Vessels, during their expansion: to which may be added, the elasticity of the Cartilages. These several stimuli can only be perceiv’d by a sentient principle, which, in the human species, is call’d the Soul. When the Soul is first united with the Body, and receives command over the organs of Motion, it seems to have been laid under a kind of necessity, by which it is compell’d to exert these organs in avoiding whatever is hurtful, and in chusing whatever is apparently beneficial, to the Body. ’Tis evident, from the laws of the Circulation, that when the Motion of the Blood through the Lungs is stop’d, for a short time, the right Ventricle of the Heart must be violently distended, and consequently severely stimulated. This strong irritation may bring the Ventricle into a vigorous contraction, which is all that is wanted to put the admirable machine again in motion; for, as soon as the right Ventricle discharges itself into the Pulmonary Artery, ’tis plain, from the laws of hydraulics, that the Blood must move in the Pulmonary Veins; and therefore the pressure on these vessels must be overcome. Thus the circulation of the Blood will be renew’d, and the vast distention of the vessels about the Heart, will rouse the attention of the Mind to change the uneasy position of the Body as soon as possible; which will alter the direction of the Heart’s center of gravity, and therefore take the pressure off the Pulmonary Veins and inferior Auricle, and by that means afford a free passage to the Blood through the Lungs. In this manner people may recover, without any external assistance.