No person, at all conversant with the phenomena of the passions, will deny the connexion between the mind and vital functions. It will therefore be only necessary to observe in answer to the third proposition; that sensation is predicated on a comparison of the past, with the present state of impressions, and that all are relative to some change in the percipient organ; heat is only sensible, because it was preceded by a lower temperature. And therefore objects which are equable in their application, and continued for a length of time, affect us but slightly; are unattended to when present, and cannot be recalled when past, must consequently escape our consciousness. Objects of minor importance operate continually on our senses, but may escape the observation when preoccupied, particles of matter passing before our eyes induce us to close the palpebræ, yet the action is not always attended to. Also the common action of the heart and arteries are not the subjects of our consciousness; the stimulus of the contained blood continuing nearly the same, conveys no impression to the mind; but let a fluid, however bland, be injected into them, and the animal will testify by its cries, the acute sensibility of the parts; or suspend their ordinary operation for a few moments, which may be readily done in some of the branches of the arterial system, and the succeeding action becomes very perceptible attended with much uneasiness and anxiety. The common action of the intestines are not generally objects of our attention, yet derange or increase that action and they establish their connexion with the sensitive medium. This is rather a species of abstract reasoning, but we have positive cases on record: in which a British colonel could suspend at pleasure the action of the heart: the stomach likewise appears under the influence of the will, as is evinced in ruminating animals, and Professor Blumenbach gives an instance of a person in whom this organ was under the strictest command; also we have from the same authority, cases in which the Iris has been subjected to the power of volition; and indeed the parrot continually displays something of the kind. For such reasons I would not consider any part of the living body independent of the common sensory, but I can suppose that the mind by disuse or disease may lose its power over some organs, as it sometimes does over even the voluntary muscles. And I can see no reason why those motions called involuntary, could not be gradually withdrawn by want of attention from the direct influence of the mind.