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portant fluid, the blood, which, from the peculiarity of its properties, has induced physiologists to maintain its vitality. This inquiry, at the same time, may meet with some assistance from observations

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the effect of certain gases, which, when introduced into the lungs, exert an influence over the blood. The pulse, for instance, of persons inhaling the nitrous oxide, though it may vary in different individuals with regard to strength or velocity, never fails to be increased in fulness; which result would intimate, that the general volume of the circulating mass is, upon the application of a proper agent, susceptible of an increasing degree of expansion. On the other hand, in the earliest stage of the noxious influence of the febrile miasma, there is an evident diminution in the volume of the blood, as is indicated by a small contracted pulse, and an increasing constriction of the capillaries. Hence may be drawn the general conclusion, that the corpuscles of the vital fuid possess within themselves an inherent dilatibility and contractility, by the alternate force of which they are enabled to act upon the elastic coats of the vessels of the human body.

A more important observation, however, with regard to the very opposite effects of the gases alluded to yet remains to be stated. It would appear, that, with an increase of the volume of the circulating fluid, a general sense of pleasure is experienced. This fact is well illustrated in the delight expressed by the individuals, who, a number of years ago, submitted themselves to the experiments instituted with the view of ascertaining the effect of the nitrous oxide. The feel

ings which they experienced are described under such terms as “ pleasurable thrillings extending from the chest to the extremities,” or “ sublime emotions." On the contrary, when there is an increasing contraction in the volume of the blood, indicated by a spastic disposition of the vessels sufficient to impede the general current of the circulating fluid, an opposite state of pain appears to be an invariable result. This fact is proved in the distressing feelings experienced during the earliest symptoms arising from the epidemic contagion of the febrile miasma.

It is on these principles, then, that I would attempt to explain the nature of the sanguineous influence or energy, as it is exercised during the course of circulation. In considering, also, the mind as simple and indivisible, as well as existing in certain states, its relation to the human frame appears to be singularly manifested by some general correspondence with the quality and degrees of these actions of the blood. We have seen, for instance, that with the peculiar influencing condition of the circulating fluid, a tendency either to pleasurable or painful feelings is in a remarkable degree connected. Proofs, therefore, may now be advanced, that with the varying force of this influence, the degree of intensity which takes place in the qualities of our mental states keeps a remarkable pace. Such evidence is afforded by a further reference to that singular compound, the nitrous oxide. When the effects of this gaseous inhalation were first tried, the general result was, that, in proportion as it influenced the circulation, sensations became more and more vivid. These were described under such terms

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as “An increased sensibility to touch,"-"A sense of tangible extension,"_" Visible impressions becoming more illuminated,”_"Luminous points arising to dazzle the vision” Hearing more acute, so that the smallest sound in the room was heard distinctly,”“ Feelings of such delight as almost to destroy consciousness.” At the same time, grateful recollections of an uncommon intensity passed rapidly through the mind. One individual, in attempting to describe his feelings, could only compare them to those which he had experienced when witnessing an heroic scene upon the stage. Another person could only refer for a description of the state of his mind to the emotions raised within his breast, when, upon the occasion of the famous commemoration held at Westminster Abbey in honour of Handel, he heard seven hundred instruments playing at one time. As a further consequence, also, of this increased degree of pleasure, time never failed to appear longer than as measured by a watch.

These observations on the mental effects arising from a strong sanguineous influence, may be extended by directing our attention, in the next place, to the febrile miasma, the primary action of which forms a direct counterpart to the salubrious agency of the nitrous oxide. At Cadiz and Malaga, this pernicious gas has been found possessing its greatest degree of virulence; having been heightened in its effects by extraordinary heat and moisture, a stagnant atmosphere, crowded multitudes, and the decomposition of human effluvia. In this state it has been received into the circulation, when the effect of the blood, thus

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chemically altered, was to vivify mental impressions to no less a degree than if the nitrous oxide had been inhaled ; at the same time, the quality of the feelings, thus rendered more intense, was of an opposite and painful kind. There was a general soreness which pervaded the whole system, of such an acuteness, that the contact of the internal air, or a new change of temperature, became insupportable. There was a distressing leipyria, or coldness of the surface of the body and of the extremities, while the interior parts felt as they were scorched with a fire. A great anxiety prevailed about the præcordia, while the images of the mind were rendered no less intense, being of such a painful description, and so increasing in their gloomy character, that they produced, as it was declared, an overwhelming dejection.

Having thus discovered in the nitrous oxide and in the febrile miasma two most important agents capable of affecting the quality of our mental feelings, we may lastly inquire into the effect which they can produce when their excitation is carried to an extreme height.

There are few of my readers, probably, who are not aware of the distinction which is always made between those states of the mind which are induced when causes impressing our organs of sense are present, and those which occur as revivals of prior mental states; the former being termed sensations, the latter ideas, or, more correctly, renovated feelings. Sensations and renovated feelings differ essentially in nothing but degree. Thus, the latter are less intense, less vivid, or fainter, than the former. This distinc

tion is acknowledged by all metaphysicians. Dr 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

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