Such is mercantile logic; and on its own conditions it is irrefragable; but it is not the custom to deal with Jenner as a tradesman, but as a man of science, and to range him with great discoverers, inventors, and benefactors of mankind; and here it is that I decidedly demur. What, I ask, did he discover? He did not discover that Cowpox prevented Smallpox: that was the dairy-maids’ faith. He did not discover that Horsegrease prevented Smallpox: that was the farriers’ faith. He did not discover that Horsegrease on milkers’ hands begot pox on cows’ teats: that was the farmers’ belief. He did not discover that inoculated virus could be conveyed from arm to arm: that was an existing practice. What then did he discover? He discovered nothing. He did no more than take the vulgar opinion of his neighbourhood to the London market. He made a few perfunctory experiments by way of confirmation, advertised them in a book, and by good or ill luck the notion was caught up, and worked to practical issues, chiefly by Pearson, who thereby incurred the full malignity of Jenner’s jealousy. The distinction between a man of science and a tradesman is this, that the mind of the one is set on the extraction of truth and the other on the extraction of profit. The man of science does not inquire what the public may be pleased to know and pay for, but he ascertains and defines what is fact, and leaves the public to adjust themselves thereto as they may find convenient. If they recognise the truth communicated, it is well for them; if they dislike or deny the truth, it is ill for them; but well or ill, the man of science is the disinterested expositor of what he knows to be true; not unfrequently, when his revelation vitally affronts popular prejudice, realising the blessing of those who are persecuted for righteousness’ sake. What therefore I maintain concerning Jenner is, that the truth (as we may presume he regarded it) he did not fully reveal; that what he did reveal, he suffered to be derided and denied; that he was content to take credit for so much of it as was marketable; whilst his private conviction about Horsegrease remained unaffected, not only in theory, but in deliberate practice. It is for me to establish these assertions.