For the variolous he recommended the substitution of the vaccine test; saying—
At the commencement of Vaccination, I deemed the Variolous Test necessary; but I now feel confident that we have one of equal efficacy, and infinitely less hazardous in the re-insertion of the vaccine lymph—
Which was to say that vaccination immediately after vaccination would be found impossible—the later practice of periodical re-vaccination being unforeseen.
Jenner might have perceived that after his proclamation of the influence of herpes on vaccination, there was nothing to be said for the variolous test. When he consented to run vaccination on the same terms as variolation, and admitted that it would be wrong to expect more from the one practice than from the other, he was bound in consistency to allow that if vaccination was frustrated by eruptions of the skin, it was matter of consequence that variolation should be frustrated by the fever of vaccination. He informed Dillwyn that he destroyed cutaneous eruptions by the application of unguentum hydrargyri nitrati, and then vaccinated with success. The smallpox inoculators did so likewise. When the irritation induced by vaccination had had time to subside, they too variolated with success.
The letter to Dillwyn, 1818, contains some other points which it is instructive to note. For example, the following passage proves two things, first, how notorious had become vaccination failures; and, second, how vaccination, from an easy art that any one might practise, had been converted into a mystery to which even “an eminent surgeon” might be unequal. Jenner says—
One word more with respect to prejudice. How frequently have we seen in the public prints paragraphs of this description—“A gentleman’s family, consisting of three or four or half-a-dozen children, were vaccinated by an eminent surgeon, and all went through the disease in the most satisfactory manner, and were pronounced safe; yet, on being exposed to the infection of the Smallpox, they all had the disease, but happily they all recovered.” Here, Sir, the mind becomes entangled with a false association. The public conceive that an eminent surgeon must be a perfect master of this little branch of our art; but it often happens that he has not stooped to look at anything beyond its outline; and when deviations arise in the progress of the pustules [as from herpes] to that extent which I have pointed out as momentous, they are passed by without attracting any particular attention.
A report having got abroad that Jenner had renounced his faith in vaccination, he replied to Dillwyn—
My confidence in the efficacy of Vaccination to guard the constitution from Smallpox is not in the least diminished. That exceptions to the rule have appeared, and that they will appear, I am ready to admit. They have happened after Smallpox Inoculation; and by the same rule, as the two diseases are so similar, they will also happen after Vaccine Inoculation.
In presence of such a declaration, it is easy to understand why the Inquiry with its supplements was kept out of print, and never referred to. His confidence in vaccination not in the least diminished! In the words cited, he surrendered afresh the claim with which he started, and for which he was paid, namely, that inoculation with cowpox rendered the constitution proof against smallpox for life, and that the protection thus afforded was without precedent in medical experience.