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and to breathe laboriously to recruit his strength.* With this excessive degree of fatigue, accelerated pulse, and difficult respiration, there is great thirst, sickness of stomach, a loathing of food, and an aversion to every species of spirituous liquor. But what is very extraordinary, these affections are as short in their duration, as they are violent.

After resting a few minutes, the sense of fatigue is so completely dissipated, that the person, in resuming his journey, feels such a renovation, that he is persuaded he will be able to prosecute it uninterruptedly. He, however, is soon disappointed. On moving a short distance only, his former inability returns, and his progress is again arrested. An additional effect of this state of the atmosphere, is an almost irresistible propensity to sleep. We are told, that if the attention of the person be not engaged, and kept excited, he will, when pausing to rest, often fall to sleep almost instantaneously, though annoyed by the wind or cold, the light or heat of the sun, and in the most incommodious and disagreeable posture of his body. This sleep, sometimes, approaches in soundness nearly to lethargy.t

Nothing affords the least relief to any of the symptoms enumerated except rest and cold water. Cordials and spirituous li. quors are found to aggravate all the complaints.

Now, in whai manner are these very singular affections to be explained? No satisfactory solution has hitherto been offered. The explanation, however, appears to me to be exceedingly obvious, and we owe it to chymical physiology.

It is clearly ascertained that respiration supports animal life, and all its actions. This process requires the presence of two principles. These are oxygen and combustible matter. The former

• These effects are not peculiar to the human species. The same writer relates, that the mules which he employed to carry his baggage, became suddenly so weak and exhausted that they could hardly walk, even when the burden was removed from their backs. They staggered as they moved; their respiration was panting and difficult, and seemingly attended with painful sensations of the chest, as they uttered plaintive and distressing cries.

† It may also be observed, that Aëronauts have generally mentioned drowsiness as one of the consequences produced by the attenuated atmosphere of the exalted regions which they explore in their excursive flights, and some have even declared that thcy slept soundly, when at the utmost pitch of their perilous adventure's.

is supplied chiefly through the medium of the lungs, and the lat. ter by the stomach. Of the vital actions, none seems to be more immediately dependent and strikingly regulated by respiration than the muscular. It is not, however, my design to dwell on the relation between them. It is sufficient for my purpose to remark, that during exercise a greater quantity of oxygen is extracted from the atmosphere by the lungs, and that carbonic acid, and water are formed, and caloric evolved in corresponding proportions. Hence it may be deduced, that during muscular exertion, there is a greater demand for oxygen, and a larger consumption of combustible matter. It also follows, if the preceding premises be admitted, as a legitimate corollary, that the same effect would be produced, namely, an exhaustion of the muscular vigour, by withholding the one or the other of these agents. In either case, fatigue will be caused, and the body rendered incapable of muscular exertion. But the incapacity in the two cases arises from different states of the system, and will be distinguished by different appearances, and removed by different methods of treatment.

Limited exercise in an atmosphere of sufficient density slowly deprives the body of its proper quantity of combustible matter until fatigue is finally induced. The body is afterwards gradually recruited by rest and food, or, directly restored to momentary strength by the use of spirituous liquors, which are pure combus. tible matter mixed with water.

But, in the elevated regions of the atmosphere where there is a deficiency of oxygen, the fatigue which comes on, is of an opposite kind. It arises from an overproportion of combustible matter, and a want of oxygen. Here, of course, it is alleviated by rest, and deep inspirations, and exacerbated by exercise, and spirituous liquors.

It is suddenly induced, because, the pulmonary system is so contrived that the body at no instant receives more oxygen than what at the instant, it requires.

We are instructed by experiments that animals placed in a vessel filled with oxygen, and respiring the gas in a state of purity, do not consume more of it than when combined with an irrespirable gas. Thus it takes an animal nearly four times as long to consume the same quantity of oxygen as atmospheric air. Richerand's Physiologr.

It is speedily removed, because, by the deep inspirations the necessary quantity of oxygen is conveyed into the system.

It is accompanied by sickness of stomach, and loathing of food, because, digestion like exercise demands a copious supply of oxy. gen.ll

It is attended by excessive thirst, because, in a rare atmosphere, there will, of necessity, be a profuse evaporation from the surface of the body.

The pulsations of the heart are more numerous, because they are performed less vigorously.

Not altogether dissimilar in its nature, or origin, though milder in its symptoms, and slower in its occurrence, is, the fatigue occasioned by immoderate exercise under the ordinary constitution of the atmosphere. In this case, we observe an increased frequency of the pulse, and of respiration, &c. &c. The cure, likewise is by rest. Cold water is found more refreshing than spirituous liquors.

There is another phenomenon connected with the present subject which deserves to be noticed. I allude to the propensity to sleep which has already been remarked. This too, can only be explained by ascribing it to a deficiency of oxygen.

Sleep, is a suspension to all, or a majority of the operations of the mind. We have not, it is true, in our possession any direct evidence to prove that the efforts of the intellect, like those of the body exact a fixed, and determinate quantity of oxygen. We had, indeed, the promise of some experiments to ascertain it by Lavoisier in an Essay, where after indicating the expenditure of vital air by muscular exercise, he undertakes to show by calculation, “ the quantity of mechanical labour exerted by the philosopher who reflects, by the man of letters who writes, or the musician who composes.!” These operations, he adds, though intellec

|| There are many facts to prove that oxygen is a principal agent in digestion and assimilation. The quantity employed in these processes seems, in some degree, to be regulated by the kind of food used. An animal diet consumes more than a vegetable one. Mr. Spalding found that when he lived upon animal food, and drank spirituous liquors, he expended the oxygenous portion of the atmosphere in his diving bell, in a much shorter time than when he subsisted on vegetable matter and water. Dr. Beddoes has also furnished some curious facts which go to establish the same conclusion. tual, have a certain dependance on the physical and material part of man, which renders them susceptible of comparison with the labours of the mechanic.

Whether these views be as just, as they are brilliant, I shall not pretend to decide. But, thcugh we may never be competent to determine with much accuracy the quantity of oxygen consumed by the operations of the mind, yet, that it is essentially necessary to the exertion of the intellectual faculties is distinctly demonstrated.

With respect to the influence of a subtraction of oxygen in the production of sleep, a few facts will be sufficient to attest it.

In the first place, we know, that the primary operation of all the irrespirable gases, and these contain no oxygen, is productive of heaviness and sleep.

Sleep is apt, moreover, to occur during the process of diges. tion, when the oxygen of the system is employed, in a considerable degree, in the assimilation of aliment, and the elaboration of chyle, or, if the disposition to sleep be counteracted, the senses, at least, become more dull, and the understanding less acute and energetic.

The production of sleep is favoured too, as has been proved, by external warmth, which lessens the supply of oxygen.

It is, from the combination of these causes, that among the inhabitants of hot climates, the custom of sleeping during the day, and especially after eating, universally prevails.

I have purposely avoided details in this inquiry, that I might not be led into prolixity.

I may, however, in a subsequent Essay dilate many parts of it with illustrations, which at present, appear in the nakedness and obscurity of insulated propositions.

CHYMISTRYFOR THE PORT FOLIO.

Nothing is more flattering to the mind of a philosopher than to observe an increasing respect for those branches of science to which he is himself partial. The chymist has therefore observed

with pleasure and pride, that the favourite objects of his pursuit, which formerly were too much despised and neglected, have of late years attracted great attention.

When the labours of chymists were directed exclusively to the discovery of the Philosopher's Stone, the Elixir of Life, and the Universal Solvent, the obloquy heaped upon them was justly merited by the sordid and visionary temper of those, whose lives were spent over the crucible and furnace. The more liberal views of modern experimenters have rescued this branch of philosophy from reproaches it never deserved, and raised it to a conspicuous rank among the sciences. In doing this they have conferred on the world, benefits, the most important. Agriculture has been improved; the arts have flourished; and medicine has been enriched by a variety of the most active and useful remedies.

The objects of investigation to the chymist, are innumerable, and the interest they excite, can only be judged of by the zeal of his inquiries. There is as much wisdom displayed in the formation of an atom, as in the creation of a world ; as much ingenuity therefore is required to unfold its properties and the laws by which it is governed. The period has arrived when the study of chymistry is no longer a reproach. It is even considered an important branch of education. An institution has been founded in London in which lectures are delivered on the interesting parts of chymistry to crowded audiences of the most respectable nobility and gentry in the British dominions.* In our own country we may hail the commencement of a taste for similar studies. Already Chymistry is taught in most of our respectable colleges, and in many private seminaries of learning; and discoveries have been made which could only have been expected from the zeal and industry of veterans in science.

One of the most interesting subjects of chymical investigation is Heat, it is one of the first objects of attention to a student of chymistry, he finds it present in all his operations; it influences all their results. One would imagine that an agent, so universally extended throughout creation, would be familiar to the whole human race, and yet we are informed that the inhabitants of the Marian island, were not acquainted with its effects till the invasion

The Royal Institution, Albemarle.strect.

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