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tion is acknowledged by all metaphysicians. Brown, for instance, remarks, that "there is a tendency in the mind to renovations of feeling less vivid, indeed, than the original affections of sense when external objects were present, but still so very similar to those primary states of the mind, as to seem almost copies of them in various degrees of vividness or faintness."

This metaphysical view being stated, I shall now once more advert to the action of the nitrous oxide on our mental feelings, from which we learn, that whenever sensations and ideas are simultaneously increased to a very great degree of vividness, the mind gradually becomes unconscious of all or most of its actual impressions, but more particularly of painful or disagreeable ones, while the recollected images of pleasurable thought, vivified to the height of sensations, appear, as it were, to take their place. "Whenever the operation of this gas," remarks Sir Humphry Davy," was carried to its greatest height, the pleasurable thrilling gradually diminished, the sense of pressure was lost, impressions ceased to be perceived, vivid ideas passed rapidly through the mind." On another occasion, this great chemist describes his feelings after the following manner:-" Immediately after my return from a long journey, being fatigued, I respired nine quarts of nitrous oxide, having been precisely thirty-three days without breathing any. The feelings were different from those I had experienced on former experiments. After the first six or seven respirations, I gradually began to lose the perception of external things, and a vivid and intense

recollection of some former experiments passed through my mind, so that I called out, What an amazing concatenation of ideas!" A third experiment by the same philosopher was perhaps attended with the most remarkable results. He was enclosed in an air-tight breathing box of the capacity of about nine cubic feet and a half, in which he allowed himself to be habituated to the excitement of the gas, which was then carried on gradually. After having, therefore, been in this place of confinement an hour and a quarter, during which time no less a quantity than 80 quarts were thrown in, he adds, "The moment after I came out of the box, I began to respire 20 quarts of unmingled nitrous oxide. A thrilling, extending from the chest to the extremities, was almost immediately produced. I felt a sense of tangible extension, highly pleasurable in every limb, my visible impressions were dazzling and apparently magnified. I heard distinctly every sound in the room, and was perfectly aware of my situation. By degrees, as the pleasurable sensation increased, I lost all connexion with external things; trains of vivid visible images rapidly passed through my mind, and were connected with words in such a manner, as to produce perceptions perfectly novel. I existed in a world of newly-connected and newly-modified ideas. When I was awakened from this semi-delirious trance by Dr Kinglake, who took the bag from my mouth, indignation and pride were the first feelings produced by the sight of the persons about me. My emotions were enthusiastic and sublime; and for a moment I walked round the room, perfectly regardless of what

was said to me. As I recovered my former state of mind, I felt an inclination to communicate the discoveries I had made during the experiment. I endeavoured to recall the ideas, they were feeble and indistinct. One recollection of terms, however, presented itself, and with the most intense belief and prophetic manner I exclaimed to Dr Kinglake, Nothing exists but thoughts, the universe is composed of impressions, ideas, pleasures, and pains.""

Such is the interesting detail of a very important physiological experiment made by one of the most adventurous as well as profound philosophers of the present age. The visionary world to which he was introduced, consisting of nothing more than the highly vivid and embodied images of the mind, and the singular laws by which such phantasms (if they may be so called) are governed, form, in fact, the real object of the present dissertation.

A singular result, but varied by the opposite quality of pain, attends the incipient influence of the febrile miasma of Cadiz and Malaga. Sensation and ideas are, as under the action of the nitrous oxide, simultaneously vivified. The mind soon becomes insensible to actual impressions, these being succeeded by a new world of ideas, of the most frightful kind. Horrid spectral images arise, the forerunner of a suddenly diminished degree of excitement, of total insensibility, or of death.

Our inquiry will now perhaps be found not wholly devoid of interest. A pathological principle in this investigation has been established, that when sensations and ideas are, from some peculiar state of the

sanguineous fluid, simultaneously rendered highly intense, the result is, that recollected images of thought, vivified to the height of actual impressions, constitute the states of the mind.

As it has now, I trust, been sufficiently shewn, that an adequate cause of spectral illusions may arise from an undue degree of vividness in the recollected images of the mind, I shall, in the next place, investigate those morbid states of the body, by which such an effect may be induced. That ideas are not unfrequently liable to be so excited as to equal in their intensity actual impressions, and thus to be mistaken for them, is a fact with which those who are in the habit of visiting the apartments of the sick cannot but be familiar. "From recalling images by an act of memory," remarks Dr Ferrier, "the transition is direct to beholding spectral objects which have been floating in the imagination;" and," adds this physician, on another occasion, "I have frequently, in the course of my professional practice, conversed with persons who imagined that they saw demons, and heard them speak; which species of delusion admits of many gradations and distinctions, exclusive of actual insanity." This observation every medical practitioner will confirm.

I may also remark, that, in pursuing the pathological inquiry in which we are engaged, our true course is at length rendered plain and direct. In judging from the operation of those peculiar gases, the nitrous oxide and febrile miasma, which, when inhaled, affect the composition of the blood, and, at the same time, exert a vivifying influence over the feelings of the

mind, it appears that our first proper object is to inquire, if there are not many morbid conditions of the body in which the blood, from its altered quality, may not produce the same consequences. In fact, the causes thus affecting the sanguineous system, may be considered as arising, in the first place, from hereditary or constitutional taints of the blood; 2dly, From the suppression of healthy or accustomed evacuations; 3dly, From adventitious matters directly admitted into the composition of this fluid; and, 4thly, From circumstances affecting the state of the circulating system through the medium of the nerves or brain. Lastly, I may be allowed to observe, that whenever such a vivifying influence can be proved to exist, no future difficulty will surely remain in accounting for the spectral illusions which must necessarily result, when ideas, from their high degree of excitement, are rendered as vivid as actual impressions.