We have seen how the Test was practised in the Cases in the _Inquiry_. Those who had undergone Cowpox were inoculated with Smallpox, and as the Smallpox did not “take,” they were assumed to be proof against that disease. Hence the absolute conclusion proclaimed _Urbi et Orbi_, that none inoculated with Cowpox could ever afterwards contract Smallpox. It was replied, that some who _had_ suffered from Cowpox _had_ contracted Smallpox, and that others _had_ received the disease by inoculation; to which Jenner’s summary answer was, “There must have been some mistake about the Cowpox; for no one _can_ have genuine Cowpox and subsequently incur Smallpox, either by infection or inoculation.” Cowpox was inoculated and propagated from arm to arm; and, in proof that the constitution was fortified against Smallpox, it was common to inoculate with Smallpox, which usually did not “take”; whereon the operator exclaimed, “Behold! the patient is insusceptible of Smallpox _for ever_!” Such was the Variolous Test. It was to multitudes absolutely conclusive; and to question its validity was to exhibit a contentious and unphilosophic disposition. What shall we now say concerning it? First, that failures were numerous in Variolous Inoculation apart from Vaccination, and that it was not supposed that when a patient did not “take,” he was therefore insusceptible of Smallpox; nor even when he did “take,” that he was thereby rendered proof against Smallpox. So many of the successfully inoculated did subsequently fall victims to Smallpox, that Variolators at the end of last century were compelled to argue (like Vaccinators at the end of this) that Variolation was a guard, but not an absolute guard; and that when it did not altogether avert Smallpox, it modified and mitigated an attack. The excuse for failure was as artful as the motive was urgent: Variolation was too good a trade to be imperilled for lack of a little ingenuity. Nevertheless, if we make full allowance on the score of frequent incapacity to receive Variolation, we have yet to explain, on a candid view of the whole evidence, how it was that in numerous cases Inoculation with Smallpox was ineffective after Inoculation with Cowpox. “What can you urge against the Variolous Test?” was a frequent and imperious demand. The explanation in general lay in the fact, that Variolation was attempted before the complete subsidence of the vaccine fever. The inoculation with Cowpox had set up a serious constitutional disturbance, and during that disturbance the Smallpox virus could not develop its malign energy. Let me show what I mean from the testimony of Jenner himself.