It is to be observed that insusceptibility to Smallpox was by no means infrequent apart from Cowpox; and as fear of Smallpox predisposes to attack, so, on the other hand, confidence in security, whether by Cowpox or other charm, would tend to exemption.
Jesty’s reasons for his experiment were thus specified--
He was led to undertake the novel practice in 1774 to counteract the Smallpox, at that time prevalent at Yetminster, from knowing the common opinion of the country ever since he was a boy (now 60 years ago) that persons who had gone through the Cowpock naturally, that is to say by taking it from cows, were insusceptible of the Smallpox.
By himself being incapable of taking the Smallpox, having gone through the Cowpock many years before.
From knowing many individuals who after the Cowpock could not have the Smallpox excited.
From believing that the Cowpock was an affection free from danger; and from his opinion that by the Cowpock Inoculation he should avoid engrafting various diseases of the human constitution, such as “the Evil, madness, lues, and many bad humours,” as he called them.
In these reasons we have the Cowpox doctrine as prevalent in Dorsetshire, which Jesty developed in family practice. The report proceeds--
The remarkably vigorous health of Mr. Jesty, his wife, and two sons, now 31 years subsequent to the Cowpock, and his own healthy appearance, at this time 70 years of age, afford a singularly strong proof of the harmlessness of that affection; but the public must, with particular interest, hear that during the late visit to town, Mr. Robert Jesty submitted publicly to inoculation for the Smallpox in the most rigorous manner; and that Mr. Jesty also was subjected to the trial of inoculation for the Cowpock after the most efficacious mode, without either of them being infected.
It is curious how evidence conforms to prepossession. Dr. Pearson and his associates were persuaded that as no one could have Smallpox twice, neither could any one have Cowpox twice. Jesty had Cowpox when young, and when at three score they found him insusceptible, they took it for granted that re-vaccination was impossible. Robert Jesty, who had Cowpox thirty-one years before was at the same time inoculated with Smallpox, and as that likewise failed to take, the experiment enforced the desired conclusion.