Little would ever be heard of objections to Vaccination, if all who undertake the responsibility of its performance, and all who feel disposed to resist its adoption, _would but thoroughly study that masterpiece of medical induction_, and imitate the patience and caution and modesty with which Jenner laid the foundations of every statement he advanced. In the first _Inquiry into the Causes and Effects of the Variolæ Vaccinæ_, Jenner set on a scientific basis the popular belief to which I have referred; and the close of the 18th Century, which had much to darken it, will be remembered till the end of human history for the greatest physical good ever yet given by science to the world.--_Papers relating to the History and Practice of Vaccination._ Pp. xi. and xii. London, 1857. These are the words of Mr. John Simon, and in them we have the Jennerian legend with the morsel of fact to the mass of fable which characterises legendary matter, ancient and modern. The recommendation to “study thoroughly that master-piece of medical induction,” Jenner’s _Inquiry_, is a mere flourish of panegyric; for, as Mr. Simon was well aware, the book had been out of print for half a century, and was practically inaccessible; whilst its reproduction has usually been considered undesirable in the interests of Vaccination, inasmuch as it reveals more than is expedient for common knowledge. An idol that is good to swear by is always fortified by a convenient obscurity. The _Inquiry_ is a quarto of less than seventy pages in large type, set in broad margins in the grand style of the period, and illustrated with four coloured plates. There are eight pages of Introductory Matter, followed by thirty-four pages of Cases, concluding with twenty-six pages of General Observations. It is to the Cases as the ground of the argument, that I would first direct attention. They are twenty-three, and may be thus assorted-- 13 of Cowpox communicated by accident. 4 of Horsegrease communicated by accident and inoculated by design. 6 of Cowpox inoculated by design or transferred from arm-to-arm. It may be tedious, but I should like to go with the reader over these Cases, for they are highly instructive. Let us take the first twelve of Cowpox communicated by accident. I.--JOSEPH MERRET, Gardener. In 1770 attended to Horses, milked Cows, and caught Cowpox. Afterwards his family had Smallpox, but he escaped. In 1795 Jenner repeatedly inoculated him with Smallpox without effect. II.--SARAH PORTLOCK, Farm Servant. In 1771 had Cowpox. In 1792 nursed her child in Smallpox “conceiving herself secure,” and was at the same time inoculated with Smallpox in both arms without effect. III.--JOHN PHILLIPS, Tradesman. Had Cowpox when nine years old. Was inoculated with Smallpox by Jenner at the age of 62 without effect. IV.--MARY BARGE, Farm Servant.