Thomson reported 556 cases in Edinburgh of which—
310 had been Vaccinated;
41 had had Smallpox; and
205 had neither been Vaccinated nor had Smallpox.
And William Gibson, surgeon at Robert Owen’s mills, New Lanark, had 322 cases, of which—
251 had been Vaccinated.
11 had had Smallpox, spontaneous or inoculated.
57 had neither been Vaccinated nor had Smallpox.
3 had had Smallpox and Cowpox simultaneously.
As is usual in epidemics of smallpox, it was the young who were the majority of sufferers; Thomson saying—
The epidemic has been observed to attack those chiefly who were under ten years of age; increasing years appearing in general to lessen the susceptibility to Smallpox contagion.
Thomson supported his opinion that chickenpox and smallpox were interchangeable varieties of variola with much cogent evidence and argument. He cited instances in which they occurred together, one constitution bringing forth chickenpox where another brought forth smallpox, whilst the infection of one appeared at times in the manifestation of the other. The controversy is not one on which it is necessary to pronounce judgment beyond saying that the whole drift of philosophic pathology is now in Thomson’s favour; and indeed at the time he wrote, his position would not have been seriously contested, save for the discredit it accumulated upon vaccination. One of Thomson’s correspondents, P. Mudie, M.D., of St. Andrews, stated the difficulty with artless force. He wrote, 18th October, 1818—
Of late years I have remarked, that the disease called Chickenpox has been much more severe than formerly; and many of the cases occurring after Vaccination, so much resembled Smallpox, that if my mind had not been prejudiced against the possibility of such an occurrence, I should have pronounced the eruption to have been of a variolous nature.
Notwithstanding his experience, Thomson held firmly by vaccination. Whilst compelled to admit that it did not avert either form of variola, he maintained with curious fervour that it made the disease milder, as if to excuse his partial surrender of faith. We all see more or less according to our prepossessions, and we need not blame Thomson if with his perspicacity he was unequal to the entire truth. The vaccinated belonged to classes who were better housed, better fed, and better cared for than the unvaccinated; and if their ailment had been measles or pneumonia in place of chickenpox, they would have all the same made better recoveries. Precisely the same error is made at this day: what is due to kindlier conditions of life is ascribed to vaccination.