What renders the Cowpox virus so extremely singular is, that the person affected with it is forever after secure from the infection of the Smallpox; neither exposure to the variolous effluvia, nor the insertion of the matter into the skin producing this distemper. (P. 7.) It is curious also to observe, that the virus, which, with respect to its effects, is undetermined and uncertain previously to its passing from the Horse through the medium of the Cow, should then not only become more active, but should invariably and completely possess those specific properties which induce in the human constitution symptoms similar to those of the variolous fever, and effect in it that peculiar change _which for ever_ renders it insusceptible of the variolous contagion. (P. 48.) And so on. The assurance was absolute, and the warrant for the assurance was the Cases adduced, and the similarity of Horsegrease Cowpox pustules and Cowpox pustules! But if the pustules were similar, the effects were not similar. Inoculation with Smallpox produced Smallpox, mild or otherwise, with pustules few or many; but inoculation with Horsegrease Cowpox was attended with no eruption beyond the points of incision-- It is an excess in the number of pustules which we chiefly dread in the Smallpox; but in the Cowpox no pustules appear, nor does it seem possible for the contagious matter to produce the disease from effluvia; so that a single individual in a family might at any time receive it without the risk of infecting the rest, or of spreading a distemper that fills a country with terror. (P. 58.) Very good; but where are we? If similarity of pustule proved the identity of Smallpox and Horsegrease Cowpox, what did those graver dissimilarities between the diseases prove? That an objection so obvious should never have occurred to Jenner indicates the extent of his logical capacity. Jenner’s expectation from the issue of the _Inquiry_ had nothing of the prophetic character described by his enthusiastic biographers. It is only necessary to peruse its pages and note the dates in order to perceive the impossibility of the vision of 1780 described by Baron when Jenner exhibited to Gardner his future glory, and how he was destined to stand like Aaron between the living and the dead until the plague was stayed. Alas! how many similar fables may we entertain because the means of detection are not, as in Jenner’s case, available. When Jenner was writing, the English people were committed to Smallpox Inoculation, or more accurately Smallpox culture, and it was in competition with Smallpox that he advanced Cowpox. “If asked,” he said, “whether his investigation be matter of mere curiosity, or whether it tend to any beneficial purpose,” he replied by setting forth the draw-backs to the existing practice, and contrasting them with the advantages of his own.