In the production of those tokens mentioned by Dr. Hodges, we know that there must have existed in the body a certain cause capable of totally destroying the parts, and reducing them to an hard eschar, similar to that produced by fire or by a caustic. As we are unacquainted with any thing capable of producing this effect but fire, we can attribute the origin of these tokens to nothing else but the emission of the latent heat of both the solids and fluids which compose these parts, and their consequent transmutation into an hard, and as it were charred, substance. That such an emission of latent heat does in some cases take place is evident from the production of a great quantity of sensible heat when certain substances are mixed together. Thus, upon mixing together oil of vitriol, oil of turpentine and strong spirit of nitre, the whole mixture will take fire and burn violently, though two of the ingredients, viz. oil of vitriol and spirit of nitre, are by themselves incapable of being inflamed. In like manner if strong spirit of nitre be poured upon oil of cloves or sassafras, the mixture will burst out into a violent flame. Water poured upon quick lime occasions great heat, and seems in great part to be converted into a solid substance; for only a small part evaporates, and the slaked lime falls into a powder to appearance perfectly dry, and from which the moisture cannot be expelled without a very violent fire. In this case Dr. Black is of opinion that the heat comes from the water, which, as we have already seen, contains a great quantity of it in a latent state. But, according to his experiments, the emission of 135 degrees of heat is sufficient to reduce water to a state of solidity; and the heat of lime when slaking is so much superior to this, that ships have frequently been set on fire by it. We must therefore either say that water in certain circumstances can part with much more than 135 degrees, or that the lime itself emits part of the heat it contains. This last indeed seems to be the more probable supposition of the two; for though fluids contain more heat in proportion to their bulk than solid bodies, we have no reason to suppose that the latter contain none at all: on the contrary the experiments formerly mentioned, especially those made by Count Rumford, show that they are furnished with an almost unlimited quantity.
The cause of the most violent kind of plague then we must suppose to be something received into the body, which in a certain time, probably sooner or later according to the strength of the contagion, disposes to an irregular emission of its heat, which coming by a kind of explosions, or, as Dr. Hodges calls them, blasts, produce those eschars which have been called tokens, and seem to be no other than partial combustions, by which the parts affected are reduced to a state of charcoal, or nearly so.
In assigning this cause for the most deadly kind of plague, we must naturally ask the question, how can all this take place without any pain? for of those who died in this manner, many felt neither pain nor uneasiness till within a few moments of death. This can only be accounted for by the sudden and perfect destruction of the parts, which did not allow time for any sensation of pain to take place; and indeed in the application of caustic for an issue, the patient often feels but little pain. It is impossible to avoid perceiving a very strong connexion between this kind of plague and the dreadful cases of spontaneous combustion related p. [182]–186. In the case of the priest indeed the fire seems to have come from without, though even this cannot be ascertained beyond a doubt; but in those who were absolutely consumed to ashes, it seems equally probable that it may have arisen from within; and as none of the unfortunate persons seem to have made any noise or struggle, the priest alone excepted, it seems probable that the first attack had deprived them of all sensation, and that, notwithstanding the terrible ideas with which such extraordinary occurrences must have inspired those who saw them, the sufferers may have died without feeling any pain. The priest seems to have felt nothing after the first stroke.
Should this cause be admitted (indeed whether it is admitted or not) we see that it is in vain to attempt to solve the phenomena of pestilence by the doctrine of stimuli, excitement or debility. There is no degree of stimulus, fire exepted, which can convert part of the body into an hard eschar, neither can it be done by any degree of debility or exhaustion. Besides, the irregular manner in which these eschars are scattered up and down, shows that the cause has not acted from a regular diffusion all over the body, but in a number of insulated spots, between which the connexion can by no means be traced. In all pestilential eruptions indeed the action of fire seems to be very perceptible. Gotwald mentions his having observed in two patients what he calls papulæ ardentes “burning pimples,” which Dr. Russel supposes to be a modification of carbuncular pustules. Gotwald calls them also fire-bladders, and says that they were as broad as a shilling, of an irregular shape, and the skin seemed as if shrivelled with fire. The carbuncle itself approaches much to the nature of the eschar, and is attended with violent heat in the adjacent parts. Gotwald, who gives an account of the plague at Dantzic, distinguishes the carbuncle into four kinds, (to be afterwards described.) Of these he says in general, that they all burn very violently at first, &c.
From all these accounts it seems plain, that in the plague there are partial discharges of heat, from some cause, upon various parts of the body; and that, in many instances, this heat destroys the texture of the parts entirely. When this is done instantaneosly the patient feels no pain, but if more gradually, the pain is excessive, as in the case of buboes and carbuncles; which the Journalist of the plague year in London informs us were attended with such horrid pain as to make the patients cry out in a lamentable manner. This extraordinary heat must either come from without or within, and we have all the reason in the world to believe that it comes from within. Mr. Hunter, in his Treatise on the Blood, informs us that in a local inflammation there is always an increase of heat in the inflamed part. Should this heat arise, as it probably does, from an emission of part of the latent heat, we may conclude, that such a quantity might be emitted, as entirely to change the texture of the parts. Thus mortifications or destructions of those parts may ensue, of all kinds, from the mild pus to the pestilential eschar.
In the effects of pestilential contagion we observe, if not a superiority, at least a different mode of action from what takes place in poisons. All these seem to act by dissolving the blood, or infecting it in such a manner that it supplies no sufficient quantity of animal spirits; of consequence, the creature soon faints and dies. In the plague, the blood does not appear to be much affected, nevertheless it emits, in various places, certain explosions which convert the parts into an eschar. Poisons always seem to produce the petechiæ or purple spots which sometimes appear in the plague. In Dr. Miller’s Treatise, already quoted, we find, among the symptoms occasioned by arsenic, “red or dark spots appearing on the skin, and rapid putrefaction, which renders speedy interment necessary.” Herein it differs from the plague, for the bodies of such as die of that distemper are not more liable to speedy putrefaction than others. Of the vegetable poisons he also observes, that, “after death, sometimes before, livid spots are observed on the body, the appearance of the blood is dark and dissolved, and putrefaction speedily takes place.” Of animal poisons—“The bite of the poisonous serpents is generally followed by tumour, and livid colour of the part bitten, extravasation of dark coloured blood into the adjacent cellular membrane, nausea and vomiting, sudden prostration of strength, paralysis of the limbs, convulsions, yellowness of the skin, hæmorrhages, &c. Livid appearances of the body, a dark coloured and dissolved state of the blood, and a rapid putrefaction, are observed after death.”
From all these accounts, however, it is plain, that, whatever may be the analogy between the action of poisons and malignant fevers, they do not in any manner operate like the contagion of the true pestilence. Of this the constant effect is to produce buboes, carbuncles, and other eruptions, resembling much more the effects of fire than any thing else; or, if the patient is cut off without the appearance of these, similar effects are observed on the internal and vital parts. Dr. Miller’s conclusion seems therefore liable to exception; in which he says, “that only the lighter cases of pestilence are unlike the effects of poison, but that, in proportion to the degree of malignity, the resemblance grows stronger.” It doth not appear that any poison hath produced one of the characteristic symptoms of the true plague, or any thing but what is common to animals dying of various diseases, the red spots on the skin only excepted.
In the eighth volume of the Philosophical Transactions abridged by Martyn, we have an account of a number of experiments by M. Deidier and others, made upon dogs into whose veins he injected, or poured into wounds made in the miserable animals, the bile of people dead of the plague at Marseilles. “The consequence was, that they became melancholy, drowsy, and without caring to eat. All of them died in three or four days, with the essential marks of the true plague, declared by buboes, carbuncles, and gangrenous inflammations in the viscera, in the same manner as in the human carcases from whence the bile was taken.”
The poisonous bile affected the creatures differently according to the vicinity of the place of injection to the heart. In the jugular vein it killed them in twenty-four hours, injected in the quantity of a drachm to two ounces of water. In this short time were brought on gangrenous inflammations, the heart was stuffed with thick and black blood, the liver was swelled, and the gall-bladder full of green bile. This shows a very essential difference between the action of the pestilential poison and that of others; the former, in some parts of the body at least, coagulates the blood; the latter, in all parts, dissolves it.
In the crural vein (the vein of the leg) the effects were less violent. In about an hour they became heavy. In the former case they instantly became drowsy. In the second experiment they contracted such a loathing for food, that they would neither eat nor drink any thing after the injection was made. On the third day there appeared considerable tumours under the axilla (the fore leg I suppose) and on their thighs, about three inches from the wound. The wound itself turned to a gangrene, and the creatures died usually on the fourth day.