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.