a supposed specific virus; no means having been adopted to ascertain the existence of the alleged evil, previous to the application of the supposed remedy. Its existence was indeed implicitly taken for granted; and reversing the usual mode of philosophising, which fixes the onus probandi upon the parties affirming any proposition, those who have denied the truth of this doctrine, or who have refused to believe it without evidence, have been required to prove a negative. In matters of science, according to the maxim, that "de quid non apparentibus, et de quid non existenbus eadem est ratio," absence of all proof of existence ought, in fairness, to be deemed sufficient proof of non-existence. But, as if pestilential contagion, instead of a matter of fact, were only a matter of faith, it has been represented as safer to believe than not to believe in its existence, without any reference to its truth or falsehood.
This doctrine throughout has been nothing but a series of gratuitous assumptions, each surpassing the other in absurdity. The number of the affected has been assumed as evidence of propagation from person to person; the fact of contact as evidence of contagion; and the cessation, or diminution of sickness, as evidence of the efficacy of sanitary precautions. With power always on their side, the adherents of pestilential contagion have been enabled to maintain their positions, without the trouble of adducing any valid proof, unfairly throwing the onus probandi, as I have said, upon their adversaries. Their endless assumptions it has been equally impossible to prove or to disprove. Disputes on controvertible assertions have necessarily terminated without any satisfactory conclusions: and their uniform results have been uncertainty and distraction, to which it did not appear that there would for a long time be an end, unless, in respect to the existence of contagion, we could succeed in proving a negative, by showing the impossibility of the affirmative. This task I have undertaken and accomplished. In my "Suggestions for the prevention and mitigation of Epidemic Diseases," &c.; in my work, entitled, "Results of an Investigation, respecting Epidemic and Pestilential Diseases, including Researches in the Levant concerning the Plague;" and in my "Sketch of Proceedings in Spain, in illustration of the invalidity of the doctrine of Pestilential Contagion, and of the destructive Effects of Quarantine or Sanitary Laws," &c. I have repeated, with additional force, my demonstrations, first promulgated in 1796 in India, of the impossibility of the existence of pestilential contagion; showing farther, that that doctrine, in an accredited form, was first promulgated, for political purposes, by the authority of the see of Rome, in 1546-7, under the pontificate of Paul III.;
