5. In certain cases the ethereal fluid quits those substances with which it is united: the air is then decomposed, the substance into which the other fluid enters is heated, or rendered more fluid than before (perhaps both) while the basis either unites itself to the moisture of the lungs, or is thrown out by the breath. Whether in any case the basis can pervade the membranes, and thus mix itself with the blood, notwithstanding the positive assertions of Dr. Girtanner and others, is very doubtful, and does not admit of any positive proof.
6. The blood, being a fluid, must be subject to the same laws with other fluids. A certain quantity of latent heat must be contained in it, in order to give the degree of fluidity naturally belonging to it. If this quantity be augmented, the fluidity will be augmented, and the blood will become thinner; if it be diminished, the contrary will take place; and if we suppose a great proportion of this latent heat to be abstracted, it is not unreasonable to suppose that something like a congelation may take place, and the blood be changed into a solid substance of such a nature as cannot any more be made to resume its former qualities.
7. By augmenting the sensible heat, the blood is affected in the same manner as any other fluid; it suffers expansion, by which the vessels are dilated in proportion, and, if this expansion and dilation be carried to a certain length, a rupture of many of the small vessels, and apoplexy, or some other grievous disease, may ensue.
8. By breathing certain kinds of air, the fluidity, heat and expansion of the blood, and of consequence the dilation of the blood-vessels, are affected. Thus, when a person breathes a quantity of the fume of charcoal, containing much fixed air, he feels himself affected with pain and a sensation of fulness in his head; he becomes sleepy, and, if the quantity be sufficiently great, he falls into an apoplexy, and dies. From dissections it appears that such as die in this manner have the capillary vessels greatly distended, and even ruptured; the heat of the body is vastly augmented, and even continues some time after death. Hence it is evident, that, by breathing this kind of air, too much sensible heat is conveyed to the blood. In like manner when we breathe the steam of water, if any quantity of that steam be condensed in the lungs, the whole quantity of latent heat contained in that steam discharges itself upon the lungs, and increases the sensible heat of the body; and from this we may learn why on some occasions our sensations should so ill correspond with the thermometer, and why a warm air almost saturated with moisture should always appear much hotter than a dry one, though the thermometer stand at an equal height in both. Oxygen air seems to convey to the blood a much larger quantity of what we have called vital spirit, than any other kind. Whether this vital spirit be the same with the latent heat of the blood, we know not; but, as this kind of air is evidently capable of supplying the blood both with latent and sensible heat, it seems most probable, that, by breathing a considerable proportion of it, both these kinds of heat, as well as the vital spirit itself, will be augmented. In this case, wherever the air naturally contains a larger quantity of oxygen than usual, the blood ought to be mere fluid, as well as warmer, than usual, provided there be no evident cause why it should be otherwise. Accordingly in warm climates it is always found that the blood is thinner and more fluid than in such as are colder; but at the same time the temperature of the body is colder than in other countries. Zimmerman tells us, that, “at Curassau, Europeans gradually lose their fresh colour and vivacity: their natural heat even becomes three or four degrees less than it was at their arrival.” The reason of this last, however, is evidently the excessive perspiration, which is more than sufficient to carry off the superabundant quantity of sensible heat thrown into the body, either by the rays of the sun, or by the superior quantity of oxygen naturally existing in the atmosphere; for it is now found, contrary to the opinions hitherto received, that in the warmer climates the atmosphere contains a larger proportion of oxygen than in the more temperate.[91]
From this discovery it appears, that, whatever may be the cause of the frequency and violence of epidemics in warm climates, it is not the want of oxygen. Nay, we should rather be tempted to think that they were produced by too great an abundance of it; and this the more especially when we know that animals confined in oxygen air are supposed to die of a burning fever; and it is likewise known that this kind of air is prejudicial to consumptive people, and even brings on the disease on those who had it not before. From the experiments mentioned in the note, it seems probable that there are but few even of swampy places in hot climates, where oxygen does not predominate; and in these the heat thrown into the blood must still be augmented by that produced from the quantity of vapour decomposed or condensed in the lungs, which, as the condensation depends upon unknown circumstances, can never be foreseen, or ever prevented, but by a removal from the place.
With regard to other kinds of air, such as inflammable, phlogisticated air, &c. experiments are yet wanting to determine their effects upon people who breathe them habitually. The proportion in which they occasionally exist in the atmosphere on particular occasions has not been ascertained, and from the experiment made by Dr. Priestley with offensive air taken from a manufactory, as well as from Dr. Chisholm just mentioned, the probability is, that, even in the most offensive places, the proportion of azote is by no means so great to the oxygen that we could suppose the excess capable of producing a disorder of any consequence, much less a violent epidemic. Fixed air is always produced in the putrefactive process, and from its quality above mentioned of rarefying and heating the blood, might reasonably be supposed to have some share in producing epidemics, were it not that this kind of air is so readily absorbed by water, as well as a number of other substances, that, except at the very moment of emission, we can scarce suppose it to have any considerable effect.
Mr. Watt in a letter to Dr. Beddoes gives an account of a kind of air, seemingly more noxious than any yet discovered, which he produced by distillation from flesh and from wool. The effects upon himself were so disagreeable that he determined to make no more such experiments, lest he should to his own hurt discover a mode of producing some grievous disease. But we cannot, from an artificial air of this kind, argue to a natural one; as the one produced by Mr. Watt was totally different from any species of air naturally known. All that we can say is, that, as far as we can trace the connexion between our bodies and the different kinds of air which may be breathed, the latter act chiefly by the heat they contain, and which they impart to the body in various proportions; by which means the latent or sensible heat of the blood, and consequently of the whole body, may be occasionally augmented or diminished. Thus the body may be considerably altered in its constitution, and rendered more liable to diseases than it was before; but still it is found that diseases continue to appear at uncertain intervals, though all the causes we are able to discover, or at least all that are constantly evident to our senses, continue to operate without intermission. Though the obvious qualities of air and climate therefore may predispose to an epidemic, we cannot affirm any thing farther: the direct cause is always different, and hath hitherto so much eluded our researches, that we can have little hope of discovering it, except by reasoning from facts less obscure.
8. In all the operations of nature which we have access to investigate, the action of electricity is so much concerned, that we can scarce suppose it to be wanting in any of them. That it is concerned in preserving the health of the human body is likewise certain, if it be the fluid which acts in the nerves, as most probably it is. But whatever preserves health will also bring on disease, if it be applied to that purpose; and we have already seen that this fluid is capable of bringing on the most dreadful symptoms, viz. mortification in its highest stage, fever, convulsions, bilious discharges, lethargy, &c. If it be capable of producing all these, can we say that it is not capable of producing those of an inferior kind, or of varying diseases and symptoms without end, according to the immense diversity of its action? It may be said that this disease was occasioned by a violent stroke of electricity, similar to lightning; but how many people have declared, that, in the beginning of some violent epidemics, they have felt a sudden stroke at the time of seizure! Dr. Hodges mentions this in the plague of 1665 at London, but treats the accounts as effects of a distempered imagination. Procopius relates the same of the plague in his time, viz. that many of the diseased felt a stroke. It is true that they said such strokes were given by spirits in human shape, in which we know they must have been deceived; but, though they were mistaken in supposing that they had been struck by a spirit, it does not from thence follow that they felt no stroke at all. The people mentioned by Dr. Hodges did not say that they were struck by a spirit, yet he treats their accounts with as great contempt as though they had. Where people have no interest in deceiving, we ought certainly to look with a favourable eye upon their testimony; for, even although some part of it should be incredible, we have still reason to believe that there is some foundation for what they say. Thus, the poor sailor, so much frightened at the sight of a large bat in New Holland, was certainly mistaken in saying that he had seen the devil; he was even mistaken in saying that he had horns;[92] but from all this it would have been doing him great injustice to say that he had seen nothing. In like manner, when numbers of people in Procopius’s time said that they were struck by spirits, when we find others in Dr. Hodges’s time saying that they were struck by some invisible agent, when we know that electricity can strike in an invisible manner, it certainly is more reasonable to conclude that violent diseases sometimes do begin by an electric stroke, than that all who said they were struck in this manner were madmen or liars.
It may now again be asked, if the plague, or violent epidemics, be produced by electric strokes, why are they not much more frequently felt, or by what are those milder diseases produced which are not accompanied by any sensible stroke? Here we can be at no loss to say, that whatever produces the highest disease, may also produce the lowest. But, besides this argument, we have positive evidence that commotions in the electric fluid will not only produce sickness, but very extraordinary and seemingly miraculous effects upon inanimate bodies. It has frequently been remarked that people are sick during the time of earthquakes, when the electric matter is in violent agitation. This has been accounted for from the motion of the earth, as the motion of a ship produces sea-sickness. But Dr. Hillary mentions a slight earthquake in Barbadoes where people were affected with sickness and vomiting for some hours after the phenomenon had ceased altogether; which undoubtedly shows, that a certain state of this fluid will disorder the human body, independent of every other circumstance, either of the heat or cold of the atmosphere, or the oxygen, hydrogen or azote contained in it. Again, we find that a certain state of the electric matter is not only capable of producing very extraordinary effects by itself, but also of communicating a power to the human body to do the same. A good number of years ago, a powder-mill near London was blown up. The explosion, as might be expected, was violent and tremendous; but the most remarkable circumstance was, that the electric matter, for a great way round, was thrown into unusual, though invisible, commotions, which discovered themselves by the rattling and breaking of china dishes though sitting apparently undisturbed upon their shelves. This phenomenon did not suddenly cease, and, during the time of it, some people appeared to be infected by an electric contagion; the power of breaking china seemed to reside in their bodies, so that if they approached or touched this kind of ware, it would instantly fly to pieces. Accounts of this extraordinary circumstance were published in many of the periodical works of the time, particularly in Dodsley’s Annual Register; and the fact seems to be established beyond controversy. It proves that what has been advanced by Dr. Priestley concerning electrical operations, on a small scale, holds good also on a large one, viz. that the fluid, when once set in motion, is not easily quieted. It establishes the fact, also, that by great explosions of gun-powder the electric matter is violently agitated; and the consequence of these agitations we cannot know. It may be said, indeed, that in the operations of nature the electric matter is often violently moved without any sickness taking place; neither in fact did any ensue at the time the powder-mill in question was blown up. But it must be remembered, that, in the ordinary course of nature, if the electric matter is moved, a receptacle is also provided for it. In a thunder-storm, where immense discharges of electricity are made from one cloud, there is another cloud of an electricity opposite to the former ready to receive them, or if not, the earth itself is frequently struck. In eruptions of volcanoes, the smoke receives the electricity discharged, and becomes charged with lightning of a more dangerous kind than that of ordinary thunderstorms; and Sir William Hamilton relates, that in the great eruption of Vesuvius, in 1794, lightning of this kind proceeded from the smoke for no less a space than seventeen days. But in artificial commotions of this fluid, where nature has not provided any receptacle, the phenomena must be quite different; and though we may with safety to ourselves interfere with the operations of fire and electricity to a certain degree, yet we may at last rouse these terrible elements into such action as will prove fatal to great numbers. Hence possibly may arise in part some of those sicknesses which take place after battles, in violent sieges, &c. An instance of this is said to have happened at Valenciennes, when last besieged by the Duke of York. A disease prevailed chiefly among women, children, and persons of a weak constitution; great numbers of whom died so suddenly that it was at first thought to be a plague, until it was found not to be infectious. The blood was found greatly dissolved, and the physicians ascribed it to the monstrous bombardment and cannonading which took place during the siege. Such was the account published in some of the newspapers of the time, and from the subsequent considerations it will not seem improbable that such things may take place.
From the experiments of Mr. Bennet (an English gentleman who has made several discoveries in electricity) it appears, that we can neither brush a piece of chalk, open or shut a book, or do several of the most trifling actions, without agitating this subtile fluid in a perceptible manner. It is well known that in some cases we cannot stroke a cat’s back without making the electric matter visible, and in some positions, by putting our fingers near the ears of the animal, very pungent sparks will be received. If then we can neither open or shut a book, if we cannot stroke a cat’s back, or approach a finger to her ear, without agitating the electric fluid, is it reasonably to think we could burn a book, or kill a cat, without doing the same? Certainly it is not. If we cannot burn a book or kill a cat without affecting this fluid, it cannot be supposed that we can burn a house or kill a man without producing a still greater commotion; and in proportion to the extent of our devastations, and the multitude of our massacres, the invisible agitation of this element must become still greater and greater. In all these transactions it must be remembered that the fluid is forced out of its natural mode of action; for electric matter is made for the preservation, not the destruction, of life: but if, by long continued and extensive application of its power to a contrary purpose, we in some measure pervert its action, no wonder that we then feel the consequences of our own proceedings by its partly turning its power against the human race altogether.