“To speak candidly I do not think that these minerals are the causes of even all those pestilences whose efficients may come from under ground”; there were many mischievous fossils of which physicians and even chymists had no knowledge, and “the various associations of these, which nature may, by fire and menstruums, make under ground and perhaps in the air itself, may very much increase the number and variety of hurtful matters.”
He makes provision, also, for the hurtful matters multiplying in their underground seats, according to a principle which we know now to be true for organic, instead of mineral matters, and to be true for them above ground, or in the air, as well as under ground:
“I think it possible that divers subterraneal bodies that emit effluvia may have in them a kind of propagative or self-multiplying power. I will not here examine whether this proceeds from some seminal principle, which many chymists and others ascribe to metals and even to stones; or (which is perhaps more likely) to something analogous to a ferment, such as, in vegetables, enables a little sour dough to extend itself through the whole mass, or such as, when an apple or pear is bruised in one part, makes the putrefied part by degrees to transmute the sound into its own likeness; or else some maturative power ... as ananas in the Indies, and medlars ... after they are gathered, acquire (as it were spontaneously) in process of time a consistence and sweetness and sometimes colour and odour, and, in short, such a state as by one word we call maturity or ripeness.”
Other of Boyle’s fruitful principles (I am separating them out from amidst much other matter not specially related to influenza) are these:
“It is possible that these effluvia may be, in their own nature, either innocent enough, or at least not considerably hurtful, and yet may become very noxious if they chance to find the air already imbued with certain corpuscles fit to associate with them.”
Again, the effluvia sent up into the air may pass by certain places without causing an epidemic, because these “are not inhabited enough to make their ill qualities taken notice of; but, more frequently, because by being diffused through a greater tract of air, they are more and more dispersed in their passage, and thereby so diluted (if I may so speak) and weakened as not to be able to do any notorious mischief.”
Again, the effluvia may not produce epidemic disease at the part of the globe where they had emerged from under ground; an illustration of which may be intended in the case of the Black Death, which, as he says, came from China, yet plague is little heard of in that country, a Jesuit, Alexander de Rhodes, who spent thirty years in those parts, testifying that the plague is not so much as spoken of there. Again, why are some epidemics of so short duration at a given place? Either, he answers, because the morbific expiration from under ground had ascended almost at once, and been easily spent; or the subterraneal commotion which sends up the miasmata “may pass from one place to another and so cease to afford the air incumbent on the first place the supplies necessary to keep it impregnated with noxious exhalation; and it agrees well with this conjecture that sometimes we may observe certain epidemical diseases to have, as it were, a progressive motion, and leaving one town free, pass on to another”—as notably in the case of sweating sickness and influenza.
Lastly there are ever new forms of epidemic disease appearing, not to count every variation of an autumnal ague “which the vulgar call a New Disease.” Of the really new types Boyle offers the following explanation: “Some among the emergent variety of exotick and hurtful steams may be found capable to disaffect human bodies after a very uncommon way, and thereby to produce new diseases, whose duration may be greater or smaller according to the lastingness of those subterraneal causes that produce them. On which account it need be no wonder that some new diseases have but a short duration, and vanish not long after their appearing, the sources or fumes being soon destroyed or spent; whereas some others may continue longer upon the stage, as having under ground more settled and durable causes to maintain them.”
As a chemist, Boyle sought for the source of the pestilential emanations in underground minerals, in the new combinations of these under the action of “fire and menstruums,” in their self-multiplying power as if by subterraneous fermentation (“which many chymists and others ascribe to metals and even to stones”), and in their meeting with suitable “corpuscles” in the air of an inhabited spot wherewith to combine for their morbific effects. He assumed, also, their discharge into the air at particular spots of the globe (where they might not be directly morbific in their effects), or in a series of localities from the wave-like progress of the underground commotion; in which assumption he seems to be applying the very old idea of classical times that earthquakes and volcanic eruptions were a cause or antecedent of epidemics. Sometimes his mineral fossils were deep in the crust of the globe, touched only by the greater cataclysms; and then we might expect novelties in the forms of epidemic disease. But he does not exclude emanations from the earth’s surface proceeding more gently or insensibly.
It would be a mistake to set aside Boyle’s hypothesis of epidemical miasmata as made altogether void by his choosing strange minerals to be the source of them, and by his assuming a kind of fermentation in these inorganic matters so as to explain the continuance and spreading of the infections. Substitute organic matters in the soil for minerals in the crust of the earth, and read a modern meaning into the doctrine of underground or aërial fermentation or leavening, and we shall find Boyle’s hypothesis, especially as applied to influenza, far from obsolete. Some such adaptation of the doctrine of miasmata was made two generations later by Dr John Arbuthnot in his ‘Essay concerning the Effects of Air upon Human Bodies,’ the immediate occasion of which was the London influenza of 1733. There is nothing to note between Boyle and Arbuthnot; for Willis and Sydenham, using the Hippocratic language of “constitutions,” explained, as we have seen, the epidemic catarrhs of the spring or winter as the reigning febrile constitution modified to suit the season and weather.